Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that the Messenger of Allah (peace and blessings be upon him) called a man from the Ansar. When he (peace and blessings be upon him) drew near his house, he heard him talking in the inner room. When he (peace and blessings be upon him) asked permission and went in to him, he did not find anyone. The Messenger of Allah (peace and blessings be upon him) said to him: "I heard you talking to someone else." He said: O Messenger of Allah, because of my fever I had become weary of people's talk and went into the inner room, and someone came in to me; after you, I have never seen anyone of more dignified company or better speech than him. He (peace and blessings be upon him) said: "That was Jibril (peace be upon him). And among you are men who, if one of them were to swear an oath by Allah, Allah would fulfil it."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12269