"...And stand before Allah with obedience [and do not speak to others during the Salat (prayers)]” (V.2:238)

Sahih al-Bukhari · Book 65 · Hadith 4534

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ إِسْمَاعِيلَ بْنِ أَبِي خَالِدٍ، عَنِ الْحَارِثِ بْنِ شُبَيْلٍ، عَنْ أَبِي عَمْرٍو الشَّيْبَانِيِّ، عَنْ زَيْدِ بْنِ أَرْقَمَ، قَالَ كُنَّا نَتَكَلَّمُ فِي الصَّلاَةِ يُكَلِّمُ أَحَدُنَا أَخَاهُ فِي حَاجَتِهِ حَتَّى نَزَلَتْ هَذِهِ الآيَةُ ‏{‏حَافِظُوا عَلَى الصَّلَوَاتِ وَالصَّلاَةِ الْوُسْطَى وَقُومُوا لِلَّهِ…

Narrated Zaid bin Arqam: We used to speak while in prayer. One of us used to speak to his brother (while in prayer) about his need, till the Verse was revealed:-- "Guard strictly the (five obligatory) prayers, especiall…