Which verse made Umar ibn al-Khattab (may Allah be pleased with him) weep when he heard it, and he said: "There is nothing after perfection but decline"?

The verse in question is the saying of Allah the Almighty: "This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion." (Al-Ma'idah: 3). Umar wept when it was revealed on the day of the Greatest Pilgrimage (Hajj al-Akbar), and the Prophet, peace and blessings be upon him, asked him the reason for his weeping. He replied that he wept because they were in a state of increase in their religion, and when something is perfected, it is not long before it diminishes. The Prophet responded to him: "You have spoken truthfully."