Chapter 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
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, especially the middle (the Best) (' Asr) Prayer and stand
before Allah with obedience (and not to speak to others during the prayers)." Then we were ordered
not to speak in the prayers.
Sahih al-Bukhari 4534