Musannaf Ibn Abi Shayba 33:183

Muhammad ibn Fudayl narrated to us, from Harun ibn Abi Wakī’, from his father, who said: When this verse was revealed: "This day I have perfected for you your religion," he said: It was the day of the Greater Hajj. He said: Then ‘Umar wept. The Messenger of Allah (may Allah bless him and grant him peace) said to him: "What makes you weep?" He said: "O Messenger of Allah, what makes me weep is that we were in an increase of our religion, but as for now that it has been perfected, nothing has ever been perfected except that it then diminished." He said: "You have spoken the truth."