Mukhtasar Bukhari (Abridged) 411 — When should followers prostrate

Narrated by Sayyiduna Bara' (bin Azib, may Allah be pleased with him): When the Prophet (peace and blessings of Allah be upon him) said "Sami' Allahu liman hamidah," none of us would bend his back (for prostration) until the Prophet (peace and blessings of Allah be upon him) went into prostration. After him, we would then go into prostration.