“Cover me up!”
Thereupon Allah revealed:
“O you who are wrapped up!
Arise and warn,
Glorify your Lord,
Purify your garments,
And shun all impurity.” (Q 74:1–5)
From that moment, revelation became intense and followed in rapid succession.

It is firmly established in the canonical sound collections—through the narration of Abū Hurayrah recorded by al-Bukhārī and Muslim, the narration of ʿUmar recorded by Muslim, and other reports—that:
A man came to the Prophet—may Allah bless him and grant him peace—wearing exceedingly white clothes and having exceedingly black hair. No trace of travel showed upon him, yet none of us recognized him. He sat before the Prophet, placed his knees against his, rested his hands on his thighs, and said,
“Tell me about Islam.”
The Prophet replied,
“Islam is to testify that there is no god but Allah and that Muhammad is the Messenger of Allah, to establish the prayer, to pay the zakat, to fast the month of Ramadan, and to make pilgrimage to the House.”
The man said, “You have spoken the truth,” and we were astonished that he would ask a question and then confirm the answer.

He then asked, “Tell me about faith (īmān).”
The Prophet said,
“It is to believe in Allah, His angels, His Books, His messengers, the resurrection after death, and to believe in destiny, its good and its bad.”
The man said, “You have spoken the truth.”

He asked about excellence (iḥsān), and the Prophet said,
“It is to worship Allah as though you see Him; for even if you do not see Him, He surely sees you.”

He then asked, “When will the Hour be?”
The Prophet answered,
“The one who is questioned knows no more about it than the questioner.”

He said, “Then tell me about its signs,” and the Prophet mentioned what he mentioned. When the man left, the Prophet said,
“Bring that man back.” They searched for him but found no trace. The Prophet then said,
“That was Jibrīl; he came to teach you your religion.”

It is also widely reported that the angel would sometimes appear to the Prophet in the likeness of Dihyah al-Kalbī, who was noted for his handsome appearance.

Allah further relates in the Quran that angels came to Abraham and then to Lot in the form of men:
“Has the story reached you of Abraham’s honored guests? When they entered upon him and said, ‘Peace,’ he replied, ‘Peace—people unknown to me.’ Then he slipped away to his family, brought a fat roasted calf, and placed it before them…” (Q 51:24-26)