He writes in his book: Al thmr Al-mustabb fi fiqh alsunnah wal kitab
The holy Prophet (PBUH) say: "Close all doors except that of Ali (AS)"
Ref: Al thmr Al-mustabb fi fiqh alsunnah wal kitab, page 487.
Also narrated by Musnad Ahmad ibn Hanbal (1/330-331), by the chain of, Abu A'wana to Abu Balaj to Amro bin Maimoon to ibn Abbas who said that he heard the Prophet (PBUH) say...
The hadith continues in next page, 488, he states:
"I say: The rest of all narrators of Ahmad ibn Hanbal are thiqat/trustworthy and that in condition of the SHEIKHAIN [i.e Bukhari and Muslim], so the chain is HASAN in my view. (also Hafiz said in Fath (7/12) that it is narrated by Ahmad bin Hanbal and Nisaie and narrators are thiqat."
Ref: Al thmr Al-mustabb fi fiqh alsunnah wal kitab, page 488.
And in these narrations, there is from ibn Umar: "That Ali ibn Abi Talib had three qualities if I had one of them it would be more dear to me than red camels: He married the daughter of the holy Prophet (PBUH), and had sons from her, doors were closed except that of him, and he was given the flag on the day of Khaibar.
It is mentioned by Ahmad ibn Hanbal (2/26) from Hasham bin Saad from Umar bin Aseed who is from narrators of muslim only, and he is truthful though he had hallucinations as said in taqreeb.
Ref: Al thmr Al-mustabb fi fiqh alsunnah wal kitab, page 491.