Greeting (prayers upon entering the masjid) while the Imam is preaching
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا مُحَمَّدٌ، - وَهُوَ ابْنُ جَعْفَرٍ - حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، قَالَ سَمِعْتُ جَابِرَ بْنَ عَبْدِ اللَّهِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم خَطَبَ فَقَالَ " إِذَا جَاءَ أَحَدُكُمْ يَوْمَ الْجُمُعَةِ وَقَدْ خَرَجَ الإِمَامُ فَلْيُصَلِّ رَكْعَتَيْنِ " .
Jabir b. 'Abdullah said that the Messenger of Allah (ﷺ) delivered the sermon and said: When any one of you comes for the Friday (prayer) and the Imam comes out (from his apartment), (even then) should observe two rak'ahs (of prayer).