Abu Qatada Al-Aslami:
Narrated Abu Qatadah al-Salmi that Allah's Messenger (Peace Be upon Him) said, "If anyone of you enters a mosque, he should pray two rak`at before sitting." (Sahih al-Bukhari, 444) (Sahih Muslim, 714)
Badr al-Din Mahmud Ayni says in his book Umdat al-Qari: Sharh Sahih al-Bukhari:
In Musanaf ibn Abi Shaybah there is another narration: "Give mosques their due rights. It was said: O Messenger of Allah, what are their due rights? He said: Two Raka'as before sitting."
Umdat al-Qari: Sharh Sahih al-Bukhari (4/202), Musanaf ibn Abi Shaybah (1/299), Sahih ibn Khuzaymah (3/162)