Musannaf Ibn Abi Shayba 1:25

Abdah ibn Sulayman narrated to us, from Juwaybir, from al-Dahhak, who said: When Hudhayfah would purify himself, 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 Allah, make me of the repentant, and make me of those who purify themselves."