"What do you think, O Abu Bakr, of two whose third is Allah" ... with these words the Prophet Mohammad -Peace and blessings upon Him- reassured his companion when they retreated in the cave Thawr, during the escape route to Medina. The Prophet and his companion retreated in a 1.25 meter high cave for three days while Qurash was searching for them.
Abu Bakr -Allah's pleasure be upon him- told the Prophet -Peace and blessings be upon him-: If any of them would look under his feet, he would see us. "He said, O Abu Bakr! What do you think about two (persons) of whom the third is Allah? ". Allah says: If you do not help him, Allah helped him (even then) when those who disbelieved drove him out as one of two; when they were both in the cave, and when he said to his companion, "Do not be sad! Surely, Allah is with us!".
This cave is located in the top of the mountain Thawr, which is 12 kilometers south of the Haram. The height of the mountain is 760 meters.
It is important to mention that in our religion it was not called to visit this cave as a worship.
 Sahih al-Buchari: Hadithno. 3653
 Quran 9:40