We used to talk while engaged in prayer and a person talked with a companion on his side in prayer till (this verse) was revealed:" And stand before Allah in devout obedience" (ii, 238) and we were commanded to observe silence (in prayer) and were forbidden to speak.
كُنَّا نَتَكَلَّمُ فِي الصَّلاَةِ يُكَلِّمُ الرَّجُلُ صَاحِبَهُ وَهُوَ إِلَى جَنْبِهِ فِي الصَّلاَةِ حَتَّى نَزَلَتْ { وَقُومُوا لِلَّهِ قَانِتِينَ} فَأُمِرْنَا بِالسُّكُوتِ وَنُهِينَا عَنِ الْكَلاَمِ