Musannaf Ibn Abi Shayba 21:133

Waki’ narrated to us, from Shu’bah, from al-Hakam, from ‘Abd al-Rahman ibn Abi Layla, from Ka’b ibn ‘Ujrah, who said: "Three [things], their sayer—or he said: their doer—will not be disappointed: he glorifies (says SubhanAllah) thirty-three times, praises (says Alhamdulillah) thirty-three times, and magnifies (says Allahu Akbar) thirty-four times at the end of every prayer." Al-Hakam said: "So I have not abandoned them ever since."