Musannaf Ibn Abi Shayba 1:20

Abdullah ibn Numayr and Abdullah ibn Dawud narrated to us, from al-A’mash, from Ibrahim ibn al-Muhajir, from Salim ibn Abi al-Ja’d, who said: When Ali finished his ablution, he would say: "I bear witness that there is no god but Allah, and I bear witness that Muhammad is His servant and His messenger. O Lord, make me among the repentant and make me among those who purify themselves."