Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1222 (DarusSalam) ⓘ

It was narrated that Ibn Mas'ud said: "We used to greet the Prophet 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.'"

أَخْبَرَنَا الْحُسَيْنُ بْنُ حُرَيْثٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَاصِمٍ، عَنْ أَبِي وَائِلٍ، عَنِ ابْنِ مَسْعُودٍ، قَالَ كُنَّا نُسَلِّمُ عَلَى النَّبِيِّ صلى الله عليه وسلم 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 عَزَّ وَجَلَّ يُحْدِثُ مِنْ أَمْرِهِ مَا يَشَاءُ وَإِنَّهُ قَدْ أَحْدَثَ مِنْ أَمْرِهِ أَنْ لاَ يُتَكَلَّمَ فِي الصَّلاَةِ ‏" ‏ ‏.‏