Sahih Muslim Book - 5, Hadith - 1203

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى أَخْبَرَنَا هُشَيْمٌ عَنْ إِسْمَاعِيلَ بْنِ أَبِى خَالِدٍ عَنِ الْحَارِثِ بْنِ شُبَيْلٍ عَنْ أَبِى عَمْرٍو الشَّيْبَانِىِّ عَنْ زَيْدِ بْنِ أَرْقَمَ قَالَ كُنَّا نَتَكَلَّمُ فِى الصَّلاَةِ يُكَلِّمُ الرَّجُلُ صَاحِبَهُ وَهُوَ إِلَى جَنْبِهِ فِى الصَّلاَةِ حَتَّى نَزَلَتْ (وَقُومُوا لِلَّهِ قَانِتِينَ) فَأُمِرْنَا بِالسُّكُوتِ وَنُهِينَا عَنِ الْكَلاَمِ.

It was narrated that Zaid bin Arqam said: "We used to speak during the prayer; a man would speak to the one next to him while they were praying, until the verse was revealed: "...And stand before Allah with obedience and do not speak to others during the Salat Then we were commanded to remain silent and forbidden to speak."