Sayyiduna Abu Sa'id Khudri رضي الله عنه narrates: We were with the Messenger of Allah صلى الله عليه وآله وسلم on the day of Jumu'ah. A Bedouin entered (the mosque) and sat behind the people, while the Messenger of Allah صلى الله عليه وآله وسلم was seated on the pulpit. The Prophet صلى الله عليه وآله وسلم asked him: Have you prayed two rak'ahs? He replied: No. The Noble Prophet صلى الله عليه وآله وسلم ordered him, so he came to an empty spot near the pulpit and performed two rak'ahs.

It is narrated from Sayyiduna Abu Qatadah (may Allah be pleased with him) that he said: I entered the mosque and the Messenger of Allah (peace and blessings be upon him) was sitting among the people, so I also sat down. But the Messenger of Allah (peace and blessings be upon him) said: What prevented you from praying two rak‘ahs before sitting down? I said: I saw you and the people sitting, so I also sat down. The Messenger of Allah (peace and blessings be upon him) said: When any of you enters the mosque, he should not sit down before praying two rak‘ahs.

(Second chain) The Messenger of Allah, peace and blessings be upon him, said: When any of you comes to the mosque, he should pray two rak‘ahs before sitting.