Greeting (prayers upon entering the masjid) while the Imam is preaching
وَحَدَّثَنَا أَبُو الرَّبِيعِ الزَّهْرَانِيُّ، وَقُتَيْبَةُ بْنُ سَعِيدٍ، قَالاَ حَدَّثَنَا حَمَّادٌ، - وَ هُوَ ابْنُ زَيْدٍ - عَنْ عَمْرِو بْنِ دِينَارٍ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، قَالَ بَيْنَا النَّبِيُّ صلى الله عليه وسلم يَخْطُبُ يَوْمَ الْجُمُعَةِ إِذْ جَاءَ رَجُلٌ فَقَالَ لَهُ النَّبِيُّ صلى الله عليه وسلم " أَصَلَّيْتَ يَا فُلاَنُ " . قَالَ لاَ . قَالَ " قُمْ فَارْكَعْ " .
Jabir b. 'Abdullah reported that while Allah's Messenger (ﷺ) was delivering the sermon on Friday a person came there, and the Messenger of Allah (ﷺ) said to him: So and so, have you prayed (two rak'ahs)? He said: No. He (the Holy Prophet) said: Then stand and pray.