Musannaf Ibn Abi Shaybah 8947 — A man who forgets the tashahhud

Al-Hasan said: If a person forgot to recite the tashahhud and left the prayer, his prayer is complete; and if he has not left the prayer, he should recite the tashahhud. According to al-Hasan, leaving the prayer means that a person speaks, or begins another prayer, or turns his face away from the qiblah.