The emissaries of Allah to His Messengers and Prophets:
Allah has told us that Jibreel (Gabriel) is the only one who carries out this mission through the verse (which means): "Say [O Muhammad]: 'Whatever is an enemy to Jibreel (Gabriel)-it is [none but] he who has brought it [i.e. the Quran] down upon your heart, by permission of Allah, confirming that which was before it and as guidance and good tidings for the believers.'" [Quran 2:97]
Revelation may be brought by angels other than Jibreel, but this happens rarely – as stated in the narration that was narrated by Ibn `Abbas who said: "Whilst Jibreel was sitting with the Prophet he heard a creaking sound above him, and he raised his head. He said: 'This is a door in the heaven which has been opened today, and it has never been opened before today, and an angel has come down through it. This is an angel who has come down to the earth, and he never came down before today. He [that angel] gave the greeting of Salaam and said: 'Rejoice, for you have been granted two lights which have not been given to any Prophet before you: the Opening (chapter) of the Book (chapter Al-Fatihah) and the closing verses of chapter Al-Baqarah. You will not read even one letter of them but you will be granted reward."' [Muslim]
According to Huthayfah the Messenger of Allah said: "An angel came to me and greeted me with salaam – he came down from the heavens and he had never come down before – and he gave me the glad tidings that Al-Hasan and Al-Husayn would be the leaders of the youth of Paradise, and that Faatimah would be the leader of the women of Paradise."" [Ibn `Asakir]
Not everyone to whom an angel comes is a Messenger or a Prophet:
Not everyone to whom an angel comes can be counted as a Messenger or a Prophet; this is an illusion. Allah sent Jibreel to Maryam (Mary), may Allah exalt her mention, as He sent him to the mother of Isma`eel (Ishmael) when she ran out of food and drink. (And it is known that neither of them were Prophets).
The companions saw Jibreel in the form of a Bedouin. And Allah sent an angel to that man who visited a brother of his for the sake of Allah, to tell him that Allah loved him because he loved his brother... This happened a lot, and the reason was to make a point.
How did the revelation come to the Messenger ?
Al-Harith Ibn Hisham asked the Messenger : "O Messenger of Allah, how does the revelation come to you?"
The Messenger said: "Sometimes it comes to me like the ringing of a bell, and that is the hardest for me. Then it departs from me, and I understand what has been said. Sometimes the angel comes to me in the form of a man who speaks to me, and I understand what he says." [Al-Bukhari]
Jibreel used to come to the Messenger in his angelic form. This was difficult for the Messenger . At other times Jibreel would change from his angelic form and take on human form, and this was easier for the Messenger .
The Messenger saw Jibreel twice in the form in which Allah created him:
Three years after the beginning of the Prophetic Mission:
The Messenger of Allah said: "Whilst I was walking, I heard a voice from the heavens. I raised my head and saw the angel who had come to me in (the cave of) Hiraa', sitting on a throne between the heavens and the earth. I was scared of him, and I went back (home) and said (to his wife), `Cover me!'" [Al-Bukhari]
When he was taken up into the heavens (the Ascension)
This occasion was mentioned in chapter An-Najm, where Allah Says (what means): "(The Quran was) Taught to him (i.e. Muhammad) by one intense in strength [i.e. Jibreel] — One of soundness. And he rose to [his] true form. While he was in the higher [part of the] horizon. Then he approached and descended. And was at a distance of two bow lengths or nearer. And he revealed to His Servant what he revealed [i.e. conveyed]. The heart did not lie [about] what it saw. So will you dispute with him over what he saw? And he certainly saw him in another descent. At the Lote Tree of the Utmost Boundary — Near it is the Garden of Refuge [i.e. Paradise] — When there covered the Lote Tree that which covered [it]. The sight [of the Prophet] did not swerve, nor did it transgress [its limit]." [Quran 53:5-17]
The mission of Jibreel :
The mission of Jibreel is not restricted only to conveying the Revelation from Almighty Allah. He used to come to the Prophet every year in Ramadaan, on every night of that month, to teach him the Quran. According to Ibn `Abbas : "The Messenger of Allah was the most generous of people, and he was at his most in generosity during Ramadaan, when he used to meet Jibreel, and he used to meet him every night during Ramadan, to study the Quran with him. The Messenger of Allah was more generous in doing good than the strong wind when it blows." [Al-Bukhari]
His leading the Messenger in prayer:
Jibreel led the Messenger Muhammad in prayer, so that he could learn the prayer as Allah wanted it to be performed. According to Ibn Mas'ood the Messenger said: "Jibreel came down and led me in prayer, so I prayed with him, then I prayed with him, then I prayed with him, then I prayed with him, then I prayed with him" — and he counted them off on his fingers five times." [Al-Bukhari]
The Messenger said: "Jibreel led me in prayer at the Ka'bah twice. He led me in praying Thuhr (noon prayer) when the sun had passed its zenith by the length of a sandal-thong, and he led me in praying Asr (afternoon prayer) when the shadow of every object was the same length as the object itself. He led me — praying Maghrib (sunsert prayer)— at the time when the fasting person breaks his fast. He led me in praying 'Ishaa' (night prayer) when the twilight had ended. And he led me in praying Fajr (dawn prayer) at the time when food and drink become Haraam (forbidden) for the one who is fasting.
On the following day, he led me in praying Thuhr when the shadow of an object was the same length as the object itself. He led me in praying 'Asr when the shadow of an object was twice as long as the object itself. He led me in praying Maghrib at the time when the fasting person breaks his fast. He led me in praying 'Ishaa' when a third of the night had passed. And he led me in praying Fajr when there was a fair amount of light. Then he turned to me and said: `O Muhammad, these are the times (observed by) the Prophets before you, and the time (for each prayer) is anywhere between these two times (mentioned in each case). "'[Abu Dawood]