Here is another Qadiani argument and its refutation. This is how they put it on one of their websites:
In his last illness, during which he died, the Holy Prophet (peace and blessings of Allah be upon him) entered the mosque with the support of two men to make the following address: “O people! I have heard that you fear the death of your Prophet. Did any Prophet before me live on so that I should be expected to live on amongst you? Listen! I am about to meet my Lord, and so will you. So I bid you to treat well the early muhajirs.” (AI-Nawar ul-Muhammadiyya min al-Muwahib lil-Dinniyya, Egypt, p. 317).
Here is the actual text of the narration with reference to the original source and truth about its authenticity.
أيها الناس بلغني أنكم تخافون من موت نبيكم هل خلِّد نبي قبلي فيمن بعث إليه فأخلد فيكم؟، ألا إني لاحقٌ بربي، وإنكم لاحقون به، وإني أوصيكم بالمهاجرين الأولين خيراً
“O people! It has reached me that you fear death regarding your prophet. Did any prophet before me live for ever that I should live forever amongst you? Lo! I am about to meet my Lord, so shall you meet Him. And I bid you to be good to the the early Emigrants.”
(Ahmad bin Muhammad Qastalani, Mawahib lil-Diniya vol.4 p.532, Makteb Al-Islami, Beirut 2004..&..Yusuf bin Ismail Nabhani’s Anwaar-i-Muhammadiya min Mahab lil-Diniya p.386, Darul Kutab Al-Ilmiyah, Beirut 1997)
Truth about the Narration:
Qastalani has not given any chain to this narration, he rather quotes it from Al-Fakihi’s Al-Fajar Al-Munir who in turn quotes it from Saif bin Umar’s book Al-Riddah wal-Futuh.
(Al-Zarqani, Sharah Mawahib lil-Diniya, vol.12 pp.110-111, Darul Kutab Al-Ilmiyah, Beirut 1996)
The same can be verified from Al-Fajar Al-Munir p.119 pub. Makteba Mishkaat Al-Islamiyah.
Scholarly views about Saif bin Umar:
Here are views of scholars about Saif bin Umar, the person whose book, Al-Riddah wal-Futuh, is the actual source of this narration:
Al-Mizi quotes the opinions of different scholars about him;
“Abbas Al-Dauri narrated from Yahya bin Ma’een:'[He is] weak in Hadith.’
Abu Hatim said: ‘[He is] Matrook (i.e. Rejected)’
Abu Dawud said: ‘He has nothing.’
Nasai’ and Darqutni said about him: ‘Weak’
Ibn Hibban said: ‘He comes up with fabricated narrations attributed to trustworthy narrators.'”
(Tehzib Al-Kamal 12/324 No. 2676)
Tirmidhi said: ‘[He is] Majhool’ (Jami’ Tirmidhi H.3866)
Ibn Hujr also quotes critical views of various scholars about him;
“Ibn Hibban accused him of heresy.
Hakim said: ‘He is accused of heresy. And he is disconnected in his narrations’
Barqani narrated from Darqutni: ‘[He is] Matrook (i.e. Rejected)'”
(Tehzib Al-Tehzib 4/259 No.517)
For this reason if you see the recent editions of the book Mawahib lil-Diniya e.g. one with research of Shaykh Salih Ahmad Al-Shaami referenced above you’ll clearly find this narration under the heading ‘Weak Hadith.’
In fact a weak narration like this coming through a person so severely criticized by the experts of the science of narration can never be reliable or brought as evidence except by those who are themselves of such character.
INDEED ALLAH KNOWS THE BEST!