Sunan an-Nasa'i 1220
It was narrated that Abdullah bin Mas'ud said:
"I used to come to the Prophet (ﷺ) when he was praying, and I would greet him with Salam, he would return my greeting. Then I came to him when he was praying, and he did not return my greeting. When he said the Taslim, he pointed to the people and said: "Allah (SWT) has decreed that in the prayer you should not speak except to remember Allah (SWT), and it is not appropriate for you, and that you should stand before Allah (SWT) with obedience.'"
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ عَمَّارٍ، قَالَ حَدَّثَنَا ابْنُ أَبِي غَنِيَّةَ، - وَاسْمُهُ يَحْيَى بْنُ عَبْدِ الْمَلِكِ - وَالْقَاسِمُ بْنُ يَزِيدَ الْجَرْمِيُّ عَنْ سُفْيَانَ، عَنِ الزُّبَيْرِ بْنِ عَدِيٍّ، عَنْ كُلْثُومٍ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ، - وَهَذَا حَدِيثُ الْقَاسِمِ - قَالَ كُنْتُ آتِي النَّبِيَّ صلى الله عليه وسلم وَهُوَ يُصَلِّي فَأُسَلِّمُ عَلَيْهِ فَيَرُدُّ عَلَىَّ فَأَتَيْتُهُ فَسَلَّمْتُ عَلَيْهِ وَهُوَ يُصَلِّي فَلَمْ يَرُدَّ عَلَىَّ فَلَمَّا سَلَّمَ أَشَارَ إِلَى الْقَوْمِ فَقَالَ ‏
"‏ إِنَّ اللَّهَ عَزَّ وَجَلَّ - يَعْنِي - أَحْدَثَ فِي الصَّلاَةِ أَنْ لاَ تَكَلَّمُوا إِلاَّ بِذِكْرِ اللَّهِ وَمَا يَنْبَغِي لَكُمْ وَأَنْ تَقُومُوا لِلَّهِ قَانِتِينَ ‏"‏ ‏.‏