Sunan Abi Dawud Book 2, Hadith 228
The Prophet (ﷺ) said: The key of prayer is purification; takbir (saying "Allah is most great") makes (all acts which break prayer) unlawful and taslim (uttering the salutation) makes (all such acts) lawful.
The Prophet (ﷺ) said: When the Imam completes the prayer and sits (for reciting tashahhud), and then becomes defiled (i.e. his ablution becomes void) before he speaks (to someone), his prayer becomes complete. And those who prayed behind him also complete the prayer.
The Prophet (ﷺ) said: Do not try to outstrip me in bowing and prostrating because however earlier I bow you will join me when I raise (my head from bowing); I have become bulky.