(20) باب الْكَلاَمِ فِي الصَّلاَةِ
It was narrated that Ibn Mas'ud said:
"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.'"
Reference: Sunan an-Nasa'i 1221
In-book reference: Book 13, Hadith 43
English translation: Vol. 2, Book 13, Hadith 1222