Musannaf Ibn Abi Shayba 1:12

Waki' narrated to us, from Zam'ah, from Salamah ibn Wahram, from Tawus, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you exits the privy, let him say: 'Praise be to Allah, who has removed from me that which harms me and has retained for me that which benefits me.'"