The Book of Prayer - Friday
7/14. Chapter:
Greeting (prayers upon entering the masjid) while the Imam is preaching
Sahih Muslim
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَخْبَرَنَا اللَّيْثُ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّهُ قَالَ جَاءَ سُلَيْكٌ الْغَطَفَانِيُّ يَوْمَ الْجُمُعَةِ وَرَسُولُ اللَّهِ صلى الله عليه وسلم قَاعِدٌ عَلَى الْمِنْبَرِ فَقَعَدَ سُلَيْكٌ قَبْلَ أَنْ يُصَلِّيَ فَقَالَ لَهُ النَّبِيُّ صلى الله عليه وسلم " أَرَكَعْتَ رَكْعَتَيْنِ " . قَالَ لاَ . قَالَ " قُمْ فَارْكَعْهُمَا " .
Jabir reported that Sulaik Ghatafani came on Friday (for prayer) while the Messenger of Allah (ﷺ) was sitting on the pulpit. Sulaik also sat down before observing prayer. The Apostle of Allah (ﷺ) said: Have you observed two rak'ahs? He said: No. He (the Holy Prophet) said: Stand and observe them
Reference : Sahih Muslim 875fIn-book reference : Book 7, Hadith 73USC-MSA web (English) reference : Book 4, Hadith 1902