Are these narrations about Istiwaa authentic?

Message: As Salaamu Alaykum dear Mufti,

What is the authenticity of these hadith:

Umm Salama (radiyallahu ‘anha) the wife of the Rasulullah (sallallahu ‘alayhi wa sallam) said: “The istiwa’ is not unknown (ghayr majhul) and its modality is inconceivable in the mind (ghayr ma`qul); one does not ask “kayf” about Him; “kayf” is inapplicable to Him.” [Ibn Hajar,Fath al-Bari 13:406-7 Beirut 1989 ed.]

Umm Salma (R.A) that she said, ‘Establishment on the Throne is not unknown the mode of it is unknown, affirming it is Iman, and denying it is kufr. [Ibn Marwiya and Laalka’i have narrated it in Kitaabus Sunnah – Fathul Bayaan vol.3 pg. 307 – Lughatul Quran vol.1 pg. 86]

Wa Alaikum Assalaam,

الجواب و بالله التوفيق

The ahadith are authentic.

The great Scholar of hadith, Hafiz Ibn Hajar Al Asqalani has mentioned in his book Fathul Baari, ‘Abul Qasim Al laa la kaa’I has mentioned in Kitaab As Sunnah from Um Salmah (R.A) that she said, ‘The Istiwaa is not unknown, and its modality is not understandable (in the mind) and affirming (confessing) it is Iman and denying it is Kufr (disbelief).’

Hafiz Ibn Hajar has also stated that Imam Baihaqi has mentioned with a good sanad from Abdullah Bin Wahab who said, ‘We were with Imam Malik (A.R) and a man came to him and said, ‘O Abu Abdullah! Ar Rahman has made Istiwa on the Arsh, how is the Istiwa? Imam Malik bowed his head in silence and them lifted his head and said, ‘Ar Rahman has made Istiwa on Al Arsh, just as he described it for himself and it shall not be asked how? To ask ‘how’ about Him is inapplicable. I do not see you except as a man of innovation. Take him out from here.’ (Fathul Baari Sharh Sahih Al Bukhari, Vol.13, Pg.406-407. (باب و كان عرشه علي الماء))

The author of Fathul Bayan Shaikh Siddeeq Bin Hasan Bin Husain Al Qanuji (1248-1309 A.H) has also narrated the tradition of Um Salma (R.A) in which she said, ‘Istiwa is not unknown and ‘Kaif’ (its how) is not understandable and affirming it is Iman and denying it is Kufr.’ (Ibn Marwiya has mentioned it). (Fathul Bayan Fi Maqasid Al Quran, Vol.4, Pg.374).

And Allah Knows Best.

Mufti Waseem Khan.

29/02/16.