Qadiani say: "In chapter 61 (As-Saff) verse 6 prophecy has been made of the advent of Mirza Ghulam Ahmad; and verses 8-10 describe the promise which was given to him."
Facts: This writing is most interesting. Verse 6 is as follows:

وَإِذْ قَالَ عِيسَى ابْنُ مَرْيَمَ يَا بَنِي إِسْرَائِيلَ إِنِّي رَسُولُ اللَّهِ إِلَيْكُمْ مُصَدِّقًا لِمَا بَيْنَ يَدَيَّ مِنَ التَّوْرَاةِ وَمُبَشِّرًا بِرَسُولٍ يَأْتِي مِنْ بَعْدِي اسْمُهُ أَحْمَدُ فَلَمَّا جَاءَهُمْ بِالْبَيِّنَاتِ قَالُوا هَ?ذَا سِحْرٌ مُبِينٌ

And its meaning, according to their English translation, is as follows: "And remember when Jesus, son of Mary, said, o children of Israel, surely I am Allah's Messenger unto you fulfilling that which is before me of Torah, and giving glad tidings of e. Messenger who will come after me. His name will be Ahmad. And when he came to them with clear proofs they said, 'This is clear enchantment"'.
The translatory of the Qadiani Swahili translation have rendered the word "Sih'r" as "udanganyifu" which means 'cheating'. But the correct translation of "Sihr" is 'magic'• or 'witch-craft', not 'cheating'.
This twisting of the words of the Qur'an has been done intentionally because Mirza Ghulam Ahmad was never called a 'magician' or 'Sihir' for the simple reason that he never showed any extraordinary sign or miracle which could be attributed to 'magic' or 'witch-craft' Of course, he was and is, branded a 'cheater': and that is why their translators have twisted the Swahili meaning of the verse, to 'This is clear cheating! Now we come to the verse itself.
Ahmad was the name of the Holy Prophet (S) of Islam. He himself told that one of his names was "Ahmad"; people during the days of Sahaba referred to him as "Ahmad" in their poems; children were named "Ahmad" after him in the same period; and Mirza Ghulam Ahmad Qadiani himself said that his followers should be called "Ahmadi" after the name of the Holy Prophet (S) of Islam who had two names Muhammad and Ahmad.

A. Sayings of the Holy Prophet
1. Jubair bin Mut'im said that the Holy Prophet (S) said; "I have five names, I am Muhammad, and I am Ahmad…… "
This tradition has been narrated by Imam Bukhari. Imam Muslim, Imam Malik and Imam Tirmizi in their books (all from Sihah as-Sitta).
2. Abu Musa Ash'ari said: The Holy Prophet (S) used to enumerate for us his names; thus he said, "I am Muhammad, and I am Ahmad ………"
This tradition is narrated in Sahih-e-Muslim, Musnad Ahmad bin Hanbal and Musnad of Al Bazzar.
3. Also it is narrated: The Holy Prophet (S) said: "Verily I was the Khatamun-Nabiyyin in the presence of Allah when Adam was in the form of the molded clay; and I am telling you its interpretation: (I am) the prayer of Abraham and good tidings of Jesus and the dream of my mother which she was shown ………."
This tradition is written in Musnad Ahmad bin Hanbal, Al-Mu'jam-ul-Kabir of Tabarani and Musnad of Al-Bazzar.
And the meaning of the phrase (good tidings of Jesus) is the same verse which the Qadianis shamelessly try to fit on Mirza Ghulam Ahmad Qadiani.
4. Also, he said: "Abraham prayed for me and Jesus brought my good tidings and my mother saw at the time of my birth a light which brightened for her all between east and west". [1]
5. Other traditions of the same meaning have been narrated in Mishkatul-Masabih.
6. The Holy Prophet (S) said: "My name in the Qur'an is Muhammad; and in Evangel is Ahmad."

B. Poems
Here are some of the poetries of the Sahaba of the Holy Prophet (S) in which the Holy Prophet (S) has been mentioned as Ahmad:
Imam Ali bin Ahmad al-Wahidi has narrated from Abu Huraira who said...............Then Ali said: "Listen to me." Then he recited telling:
"People surely know that my share in the Islam is much greater than all shares; and Ahmad the Prophet (S) is my brother and father in law and cousin, May Allah bless him".
This tradition is narrated by Qadhi Maybadhi Shafei and Sheikh Al-Qanduzi Hanafi from Imam Wahidi, (Vide Yanabiul-Mawaddah. p.68).
(b) Imam Ali (a.s.), during the days of his Caliphate said, condemning some of the allegations of his enemies: "Lo, I heard an evil talk, which is a lie on Allah and which turns the color of hair into white; which enters into the ears and covers the eye. Ahmad would not have been pleased if he were informed of it".
Al-Imamah was'siyasah (Vol.I, p.84); Kitab ussiffin of Ibn Muzahim, p.24; Sharh-Ibn Abil Hadid (Vol.2, p.69).
(c) Amr bin ‘As, before accepting Islam, was one of the greatest enemies of Islam. In those days, he boasted of that enmity. It was in that connection that he said about himself: "And (I am) the enemy of Ahmad from among them; and am the most out-spoken person, against him" (Tazkira Sibt Ibn Jawzi, p.16; Sharh Ibn Abil Hadid Vol.6, p.292; Jamharatul-Khutub, Vo1.2, p.12).
(d) Hassan bin Thabit Ansari, the famous poet of the Holy Prophet (S) said,
"There are forever from the family of Hashim the• unassailable pillars, of strength in Islam and its pride. The virtuous chiefs, among whom is Ja'afar and his brother Ali (a.s.) and from them is Ahmad, the chosen one". (Al-Iqdul-Farid of lbnu Abde Rahbih Al-Undulusi, Vol.5, p.380, printed in Egypt).
(c.) Name: People from the beginning used to name their children Ahmad after the name of the Holy Prophet (S). For example, Imam Hassan, the grandson of the Holy Prophet (S), (died 50 A.H.) had named one of his sons 'Ahmad'. (Bihar-ul-Anwar, Vol.10).
(d) And Mirza Ghulam Ahmad himself writes: And Ahmad is that name of the Holy Prophet (S) which was mentioned by Prophet Jesus: "will come after me, his name is Ahmad". The word
'After Me' shows that prophet would come after me without any gap, i.e., no other prophet would come between me and him". (Kitab Malfuzate•Ahmad, i.e., Diary 1901 pp. 4 and 5. Akhbar Al-Hakam dated 31/1/1901).
Ponder seriously upon the italicized sentence which is a complete proof in itself.
Thus Mirza Ghulam Ahmad himself accepts that this verse is the prophecy of our Holy Prophet (S), who was to come after Prophet Jesus (a.s.)
"without gap". Remember that this is the qualification of the Holy Prophet (S) of Islam and not of Mirza Ghulam Ahmad Qadiani.
(e) Again he writes: "And this sect has been named Ahmadiyya because our Prophet (peace be on him) had two names; 1. Mohammad (S) and 2. Ahmad (S)" (Ishtihar Wajibul Izhar, 4/11/1900).
(f) Again he writes: "You have heard that our Prophet (S) had two names One, Mohammad (S) and this name is written in Torah the second name is Ahmad (S) and this name is in Evangel….... As appears from this verse: "And giving good tidings of a Messenger who will come after me whose name is Ahmad". (Arbain No.4, p.13).
(g) And the name of your prophet was Ghulam Ahmad, not Ahmad. And he himself has written its meaning as 'slave of Ahmad', as will appear in these writings: "Because the Christian missionaries turned Jesus, son of Mary, into god and abused our Chief, Maula and real Shafi (i.e., the Holy Prophet Muhammad S.) and made the earth unclean by abusive books, therefore, in contrast to that Messiah who was called god, God sent in this Ummah a promised Messiah who is far greater in all his glories than the first Messiah (i.e. Prophet Jesus a.s.) and He (i.e., God) named this second, Messiah "Ghulam Ahmad", so that it may be a sign that what type of god was the Messiah of the Christians who cannot compete with even a 'humble slave of Ahmad'. I mean, how is that Messiah who is inferior 'to the 'slave of Ahmad' in his nearness and Shifa'at."
"The Christians were proclaiming loudly that the Messiah also is unique without any partner in his nearness and honor. Now God shows that, 'look, I will create his second who is better than him; (and) who is 'Ghulam Ahmad' i.e., slave of Ahmad'.
If you want to know the true meaning of; trying to extinguish the light of Allah by the puff of mouth look at the Qadianis' attempts which if successful would mean that the Holy Prophet (God forbid) wrongly claimed to be Ahmad!
It is really surprising to see the Qadianis ignoring the meaning of "Ghulam Ahmad" which the holder of the name himself reiterates repeatedly, especially so when that holder is also their prophet. To prove their own view (and, in the process, refuting the meaning given by Mirza Ghulam Ahmad Qadiani himself) they argue that "Ghulam Ahmad" has no vowel of "possession". Had it been Arabic, it, should have been "Ghulam-o-Ahmad";
or if Persian, then it should have been "Ghulam-e-Ahmad'.
All right, let us talk to them in their own way. It is Persian combination and in Persian language, many possessive phrases whose first part denotes some kind of relation (like 'bin' - son - , 'pisar' - son -, 'saheb' - owner or companion) are used without the possessive vowel. This system is called 'Fakk-e-Izzafat (i.e., omission of possessive vowel).
Examples are: Saheb-dil, Pidar-zan, Pisar-Am, etc. This happens because of the frequency of use. Likewise, because of frequent use, the possessive vowel in such names as "Ghulam Ahmad" is omitted, but the meaning remains the same. Ask anyone having a name like "Ghulam Rasul" or "Ghulam Husain" and he will at once say that his name means "slave of the Prophet" or "slave of Husain".

Note:
[1] Al-Iqdul-Farid, Vol. IV, p. 251.