A fellow Sunni brother told me that Abu Bakr was in the same cave as the Holy Prophet (PBUH). Is there not Qur’anic reference to this incident and a certain companion being advised not to be afraid? Would you please provide me with the entire ayah and reference.

The ayah which refers to this incident is:

If you do not help the Holy Prophet, [it is of no consequence] for Allah helped him when the disbelievers expelled him. He was the second of the two, they were in the cave and he said to his companion, ‘Do not fear. Truly Allah is with us. Qur’an 9:40

The Holy Prophet’s companion, Abu Bakr, became frightened in the cave, and cried out in anguish when he heard the enemy nearby. The Prophet (PBUH) quietened him saying, ‘Don’t be frightened, Allah is with us’.