"We used to greet the Prophet ﷺ with salam and he would return our salam, until we came back from the land of Ethiopia. I greeted him with salam and he did not return my greeting,a nd I started to wonder why. So I sat down; and when he finished praying, he said: 'Allah (SWT) decrees what He wills, and He has decreed what we should not speak during the prayer.'"
كُنَّا نُسَلِّمُ عَلَى النَّبِيِّ ﷺ فَيَرُدُّ عَلَيْنَا السَّلاَمَ حَتَّى قَدِمْنَا مِنْ أَرْضِ الْحَبَشَةِ فَسَلَّمْتُ عَلَيْهِ فَلَمْ يَرُدَّ عَلَىَّ فَأَخَذَنِي مَا قَرُبَ وَمَا بَعُدَ فَجَلَسْتُ حَتَّى إِذَا قَضَى الصَّلاَةَ قَالَ إِنَّ اللَّهَ ﷻ يُحْدِثُ مِنْ أَمْرِهِ مَا يَشَاءُ وَإِنَّهُ قَدْ أَحْدَثَ مِنْ أَمْرِهِ أَنْ لاَ يُتَكَلَّمَ فِي الصَّلاَةِ