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 (Subhanahu-wa-Taala) has decreed that in the prayer you should not speak except to remember Allah (Subhanahu-wa-Taala), and it is not appropriate for you, and that you should stand before Allah (Subhanahu-wa-Taala) 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 ﷺ 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 " .