Sahih al-Bukhari Book 62, Hadith 44
We were with the Prophet (ﷺ) while he was holding `Umar bin Al-Khattab by the hand.
While I was with the Prophet (ﷺ) in one of the gardens of Medina, a man came and asked me to open the gate. The Prophet (ﷺ) said to me, "Open the gate for him and give him the glad tidings that he will enter Paradise." I opened (the gate) for him, and behold! It was Abu Bakr. I informed him of the glad tidings the Prophet (ﷺ) had said, and he praised Allah. Then another man came and asked me to open the gate. The Prophet (ﷺ) said to me "Open (the gate) and give him the glad tidings of entering Paradise." I opened (the gate) for him, and behold! It was `Umar. I informed him of what the Prophet (ﷺ) had said, and he praised Allah. Then another man came and asked me to open the gate. The Prophet (ﷺ) said to me. "Open (the gate) for him and inform him of the glad tidings, of entering Paradise with a calamity which will befall him. " Behold ! It was `Uthman, I informed him of what Allah's Messenger (ﷺ) had said. He praised Allah and said, "I seek Allah's Aid."
The Prophet (ﷺ) entered a garden and ordered me to guard its gate. A man came and asked permission to enter. The Prophet (ﷺ) said, "Admit him and give him the glad tidings of entering Paradise." Behold! It was Abu Bakr. Another man came and asked the permission to enter. The Prophet (ﷺ) said, "Admit him and give him the glad tidings of entering Paradise." Behold! It was `Umar. Then another man came, asking the permission to enter. The Prophet (ﷺ) kept silent for a short while and then said, "Admit him and give him the glad tidings of entering Paradise with a calamity which will befall him." Behold! It was `Uthman bin `Affan. `Asim, in another narration, said that the Prophet (ﷺ) was sitting in a place where there was water, and he was uncovering both his knees or his knee, and when `Uthman entered, he covered them (or it).