The Book of Prayer - Friday
7/14. Chapter:
Greeting (prayers upon entering the masjid) while the Imam is preaching
Sahih Muslim
وَحَدَّثَنِي مُحَمَّدُ بْنُ رَافِعٍ، وَعَبْدُ بْنُ حُمَيْدٍ، قَالَ ابْنُ رَافِعٍ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، أَخْبَرَنِي عَمْرُو بْنُ دِينَارٍ، أَنَّهُ سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ، يَقُولُ جَاءَ رَجُلٌ وَالنَّبِيُّ صلى الله عليه وسلم عَلَى الْمِنْبَرِ يَوْمَ الْجُمُعَةِ يَخْطُبُ فَقَالَ لَهُ " أَرَكَعْتَ رَكْعَتَيْنِ " . قَالَ لاَ. فَقَالَ: «ارْكَعْ».
Jabir b. 'Abdullah reported that a person came (in the Mosque) while the Messenger of Allah (ﷺ) was delivering the sermon on Friday (standing) on the pulpit. He (the Holy Prophet) said to him: Have you offered two rak'ahs? He said: No. Upon this he said: Then observe (them).
Reference : Sahih Muslim 875dIn-book reference : Book 7, Hadith 71USC-MSA web (English) reference : Book 4, Hadith 1900