Sahih al-Bukhari, Book 11, Hadith 55 (In-Book) ⓘ
Narrated Jabir: A man entered the Mosque while the Prophet was delivering the Khutba. The Prophet said to him, "Have you prayed?" The man replied in the negative. The Prophet said, "Pray two rak`at."
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 ".
also referenced under: Hadith 931 (DarusSalam) & Volume 2, Book 13, Hadith 53 (USC-MSA)