A non-Muslim researcher is asking about the proof that Jibreel spoke to the      Prophet  (peace and blessings of Allaah be upon him)
Question

I'm a student of a college in the USA. This question is for my paper of Western Civil class. What proof do you have that Gabriel spoke to Muhammad?
Praise be to Allah.Jibreel (peace be upon him) spoke to Muhammad (peace and blessings of Allah be upon him) directly, with no barrier in between, and the Prophet Muhammad (peace and blessings of Allah be upon him) saw him in his true form. This was reported in many aayaat (verses of the Quran) and ahaadeeth (reports of the things that the Prophet Muhammad (peace and blessings of Allah be upon him) said and did).
 1.Allah says (interpretation of the meaning):
 “By the star when it goes down (or vanishes).
Your companion (Muhammad) has neither gone astray nor has erred.
Nor does he speak of (his own) desire.
It is only a Revelation revealed.
He has been taught (this Quran) by one mighty in power [Jibreel (Gabriel)].”
[al-Najm 53:1-5]
 The mufassireen (commentators on the Quran) have stated that what is meant by “one mighty in power” is Jibreel (peace be upon him), who taught Muhammad (peace and blessings of Allah be upon him) the Revelation. One of the ways in which Revelation happened is when the angel spoke directly to the Prophet. This indicates that Jibreel (peace be upon him) spoke to Muhammad (peace and blessings of Allah be upon him). This idea is also supported by the aayahs (interpretation of the meaning):
 “And truly, this (the Quran) is a revelation from the Lord of the ‘Aalameen (mankind, jinn and all that exists),
Which the trustworthy Rooh [Jibreel (Gabriel)] has brought down
Upon your heart (O Muhammad) that you may be (one) of the warners,
In the plain Arabic language”
[al-Shu’araa’ 26:192-195]
 “Say (O Muhammad): “Whoever is an enemy to Jibreel (Gabriel)(let him die in his fury), for indeed he has brought it (this Quran) down to your heart by Allah’s Permission, confirming what came before it [i.e. the Tauraat (Torah) and the Injeel (Gospel)] and guidance and glad tidings for the believers”
[al-Baqarah 2:97]
 2.The First Revelation, as is well known, happened when the Prophet (peace and blessings of Allah be upon him) was in seclusion in the cave of Hiraa’. Jibreel (peace be upon him) came to him and commanded him to read.It was narrated that ‘Aa’ishah the Mother of the Believers (may Allah be pleased with her) said:
“The first of the Wahy (Revelation) that came to the Messenger of Allah (peace and blessings of Allah be upon him) was seeing true dreams; he never saw any dream but it came true like the break of day. Then the love of seclusion was bestowed upon him. He used to go into seclusion in the cave of Hiraa’ where he would worship Allah continuously for many nights, until he went back to see his family to collect more provisions. He would go back to Khadeejah, and take provisions with him for a similar number of nights. (This went on) until the truth came to him when he was in the cave of Hiraa’. The angels came to him and said, ‘Read!’ He said, ‘I am not a reader.’ He [the Prophet (peace and blessings of Allah be upon him)] said: he embraced me and squeezed me so hard that I almost could bear it no longer, then he released me and said, ‘Read!’ I said, I am not a reader.’ Then he embraced me a second time and squeezed me so hard that I almost could bear it no longer, then he released me and said, ‘Read!’ I said, I am not a reader.’ Then he embraced me a third time and squeezed me so hard that I almost could bear it no longer, then he released me and said, ‘Read! In the Name of your Lord Who has created (all that exists). He has created man from a clot (a piece of thick coagulated blood). Read! And your Lord is the Most Generous.’ [al-‘Alaq 96:1-3 – interpretation of the meaning]. Then the Messenger of Allah (peace and blessings of Allah be upon him) came back with (the Revelation) and with his heart pounding wildly.” (Narrated by al-Bukhaari, no. 3; Muslim, no. 231).
3.It was narrated from ‘Aa’ishah (may Allah be pleased with her) that al-Haarith ibn Hishaam (may Allah be pleased with him) asked the Prophet (peace and blessings of Allah be upon him), “O Messenger of Allah, how does the Revelation come to you?” The Messenger of Allah (peace and blessings of Allah be upon him) said: “Sometimes it comes to me like the ringing of a bell, which is the hardest of all, then it passes once I have grasped what is said. And sometimes the angel comes to me in the form of a man and speaks to me, and I grasp what he says…” (Narrated by al-Bukhaari, no. 2).
4.The lengthy hadeeth about Jibreel, when he came in the form of a man, a stranger, and sat down with the Prophet (peace and blessings of Allah be upon him) and asked him about Islam, Eemaan (faith) and Ihsaan (goodness, perfection). The Messenger (peace and blessings of Allah be upon him) answered his questions, knowing that he was Jibreel. When he had finished asking his questions and had gone away, the Prophet (peace and blessings of Allah be upon him) told his companions that this was Jibreel, who had come to teach them their religion. See Saheeh al-Bukhaari, no. 48; Muslim, no. 9.
5.The reports about the Israa’ and Mi’raaj (Prophet’s night journey from Makkah to Jerusalem, and ascent from Jerusalem into the seven heavens). The Prophet (peace and blessings of Allah be upon him) asked Jibreel questions, and Jibreel answered him. See Saheeh al-Bukhaari, no. 2968; Muslim, no. 238, and the ahaadeeth which tell the story of the Israa’ and Mi’raaj.
6.There are also many ahaadeeth in which the Prophet (peace and blessings of Allah be upon him) says, “Jibreel came to me and said…”, such as the hadeeth in which he (peace and blessings of Allah be upon him) said: “Jibreel (peace be upon him) came to me and said, ‘Whoever among your ummah (nation) dies notassociating anything with Allah, will enter Paradise.’ I said, ‘Even if he does such and such?’ He said, ‘Yes.’” (Narrated by al-Bukhaari, no. 2213; Muslim, no. 137)
When the Messenger of Allah (peace and blessings of Allah be upon him) came back from (the battle of) al-Khandaq, he and his companions put down their weapons and washed themselves. Jibreel came to him with his head covered with dust and said, “You have put down your weapons! By Allah, I have not put down mine.” The Messenger of Allah (peace and blessings of Allah be upon him) said, “Where to?” He said, “Over there” – and pointed towards Bani Qurayzah. So the Messenger of Allah (peace and blessings of Allah be upon him) set out [to resume the campaign]. (Narrated by al-Bukhaari, no. 2602; Muslim, no. 3315).
 And there is more, similar, evidence. And Allah knows best.