Musnad Ahmad 25:1268

Hashim narrated to us, Abu Bishr informed us, from Sa'id ibn Jubayr, from Ibn Abbas, who said: Umar ibn al-Khattab used to grant permission to the people of Badr, and he would grant permission to me along with them. Some of them said: "He grants permission to this youth along with us, while we have sons like him?" Umar said: "He is of those whom you know." He said: So he granted them permission one day, and he granted me permission along with them. He asked them about this surah: "When the victory of Allah comes and the conquest" (110:1). They said: "Allah commanded His Prophet, may Allah bless him and grant him peace, that when it is conquered for him, he should seek His forgiveness and repent to Him." He said to me: "What do you say, O Ibn Abbas?" I said: "It is not as they say, but rather He informed His Prophet, peace and blessings be upon him, of the approach of his death. He said: 'When the victory of Allah comes and the conquest'—the conquest of Makkah—'and you see the people entering into the religion of Allah in multitudes'—that is the sign of your death—'so glorify the praise of your Lord and seek His forgiveness; indeed, He is ever Accepting of repentance.'" He then said to them: "How can you blame me for what you see?"