Musnad Ahmad 32:1871

Ahmad ibn Abd al-Malik narrated to us, Nuh ibn Qays al-Haddani narrated to us, Khalid ibn Qays narrated to us, from Qatadah, from Anas, who said: A man came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, inform me of what Allah has obligated upon me regarding prayer." He said: "Allah has obligated upon His servants five prayers." The man said: "Is there any before them or after them?" He said: "Allah has obligated upon His servants five prayers." He said it three times. The man said: "By the One who sent you with the truth, I will not add anything to them, nor will I decrease anything from them." The Prophet, may Allah bless him and grant him peace, said: "He has entered Paradise if he is truthful."