I've read that before Islam began, "Muhammad adopted the practice of praying alone for several weeks every year in a cave"...But to WHOM?

I have visited the Mecca and seen the Mountain Hira and Noor. Prophet Muhammad the first verse Iqra revealed to him at the Hira cave and thereafter he was trained by the angel Israfeel for three months he does not received any revelation. Angel Gabriel guided and trained him because he was the prophet and messenger of the God. Still those exists in the city Mecca.

Muhammad peace be upon him was praying to the creator, He was following prophet Abraham peace be upon him. Prophet Abraham was Muslim, (submits his will to the creator), and he is the one who named us Muslims. Quran: 3:67 "Abraham was neither a Jew nor a Christian, but he was a Monotheist, a Muslim. And he was not of the Polytheists."

Prophet Muhammad peace be upon him never had in his all life idol worshipping.

He wasn't praying but meditating and contemplating.

http://www.al-islam.org/life-muhammad-prophet-sayy...

"Muhammads father, Abdullah and his mother, Amina were both pagans and they used to worship many idols. His entire childhood (probably up to his teen) was spent in paganism."

http://www.inthenameofallah.org/Muhammad%20the%20P...

His first revelation (in the cave) he thought was from a devil and he freaked out and was going to jump off a cliff but his wife talked him out of it...

Once the prophet he worshipped along side pagans when he couldn't over come them and to get out of it claimed the devil gave him revelations. these verses were abrogated. (Satanic verses of the koran)

"By the Star when it sets, your comrade does not err, nor is he deceived; nor does he speak out of (his own) desire..."

and when he came to the words:

Have you thought upon "al-Lat" and "al-Uzza" and "Manat", the third, the other? < 3 Pagan gods

Satan cast on his tongue, because of his inner debates and what he desired to bring to his people, the words:

"These are the high flying cranes; verily their intercession is accepted with approval.

http://www.answering-islam.org/Responses/Saifullah...

As requested by popular demand...

1) Tabari VI.107 : SATAN CASTS A FALSE REVELATION ON THE MESSENGER OF ALLAH'S TONGUE

The messenger of Allah was eager for the welfare of his people and wished to effect a reconciliation with them in whatever ways he could. It is said that he wanted to find a way to do this, and what happened was a follows. (This section is also omitted by Ibn Hisham, perhaps because he felt it was discreditable to Muhammad).

Ibn Humayd - Salamah-Muhammad b. Ishaq - Yazid b. Ziyad al-Madani - Muhammad b. Ka'b al-Qurazi: When the messenger of Allah saw how his tribe turned their backs on him and was grieved to see them shunning the message he had brought to them from Allah, he longed in his soul that something would come to him from Allah which would reconcile him with his tribe. With his love for his tribe and his eagerness for their welfare it would have delighted him if some of the difficulties which they made for him could have been smoothed out, and he debated with himself and fervently desired such an outcome. Then Allah revealed:

53:19 "By the Star when it sets, your comrade does not err, nor is he deceived; nor does he speak out of (his own) desire..."

and when he came to the words:

53:20 Have you thought upon al-Lat and al-Uzza and Manat, the third, the other?

Satan allegedly cast on his tongue, because of his inner debates and what he desired to bring to his people, the words:

53:21 "These are the high flying cranes;

53:22 verily their intercession is accepted with approval. (An alternative reading to turtada is turtaja, meaning, "is to be desired or hoped for")

When Quraysh heard this, they rejoiced and were happy and delighted at the way in which he spoke of their gods, and they listened to him, while the Muslims, having complete trust in their prophet in respect of the messages which he brought from Allah, did not suspect him of error, illusion, or mistake. When he came to the prostration, having completed the surah, he prostrated himself and the Muslims did likewise, following their prophet, trusting in the message which he had brought and following his example. Those polytheists of the Quraysh and others who were in the mosque likewise prostrated themselves because of the reference to their gods which they had heard, so that there was no one in the mosque, believer or unbeliever, who did not prostrate himself. The one exception was al-Walid b. Al-Mughirah, who was a very old man and could not prostrate himself; but he took a handful of soil from the valley in his hand and bowed over that. Then they all dispersed from the mosque. The Quraysh left delighted by the mention of their gods which they had heard, saying, "Muhammad has mentioned our gods in the most favorable way possible, stating in his recitation that they are the high flying cranes and that their intercession is received with approval."

*** The sacred area around the Ka'ba was not, of course, an 'Islamic' mosque at this period, though the word masjid, 'place of prostration, mosque' is applied to it in the daus of paganism, because in reality thast is exactly what they used to do long before Muhammad and his version of Islam***

The news of the prostration reached those of the messenger of Allah's companions who were in Abyssinia and people said, "The Quraysh have accepted Islam." Some rose up to return, while others remained behind. Then Gabriel came to the Messenger of Allah and said, "Muhammad, what have you done? You have recited to the people that which I did not bring to you from Allah, and you have said that which was not said to you." Then the messenger of Allah was much grieved and feared Allah greatly, but Allah sent down a revelation to him, for He was merciful to him, consoling him and making the matter light for him, informing him that there had never been a prophet or a messenger before him who desired as he desired and wished as he wished but that Satan had cast words into his recitation, as he had cast words on Muhammad's tongue. Then Allah cancelled what Satan had thus cast, and established his verses by telling him that he was like other prophets and messengers, and revealed:

53:19 Have ye thought upon al-Lat and al-Uzza

53:20 And Manat, the third, the other? (53:19,20)

Then, originally, the verses (known today as the satanic verses) followed:

53:21 These are the exalted cranes (intermediaries) [Gharaniq]

53:22 Whose intercession is to be hoped for.

The cranes whose intercession was recognized were, of course, the three deities. The same accounts tell us that after this revelation was completed, Muhammad, his followers and the pagan Arabs all prostrated. Tensions eased, reconciliation was at hand, and all were delighted.

But Muhammad soon retracted the reconciliation—how soon is not clear. For the account continues that Gabriel, the angel of revelation, informed Muhammad that Satan had used Muhammad's desire for reconciliation with the pagan leaders to insert into the revelation of Allah the verses about the interceding cranes, otherwise called the" Satanic Verses". The verses which follow, ABROGATED / OVERTURNED the satanic verses, serve as the current reading of the Quran.