Sahih al-Bukhari 931
Sahih al-Bukhari · Book 11: Friday Prayer · When the Imam is delivering the Khutba, a light two Rak'a Salat (prayer) (Tahayyat-ul Masjid)
Narrated Jabir:
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ ، قَالَ حَدَّثَنَا سُفْيَانُ ، عَنْ عَمْرٍو ، سَمِعَ جَابِرًا ، قَالَ دَخَلَ رَجُلٌ يَوْمَ الْجُمُعَةِ وَالنَّبِيُّ صلى الله عليه وسلم يَخْطُبُ فَقَالَ " أَصَلَّيْتَ ". قَالَ لاَ. قَالَ " فَصَلِّ رَكْعَتَيْنِ " .
A man entered the Mosque while the Prophet (ﷺ) was delivering the Khutba. The Prophet (ﷺ) said to him, "Have you prayed?" The man replied in the negative. The Prophet (ﷺ) said, "Pray two rak`at."