Musannaf Ibn Abi Shayba 21:18

Abu Bakr narrated to us, he said: Waki' narrated to us, from Uthman al-Shahham, from Muslim ibn Abi Bakrah, from his father, from the Prophet (may Allah bless him and grant him peace), that he used to supplicate at the end of the prayer, saying: "O Allah, I seek refuge in You from disbelief, poverty, and the punishment of the grave."