In Mahabaratha there was a circumstance where Hanuman met Bheema. Any evidence supporting this statement from Hinduism scriptures. Who was the cause for this meeting?
The cause for the meeting was Bheem. As we know that Lord Varun was godfather for both Lord Hanuman and Bheem. Bheem being one of the strongest at that time was very proud of his strength.To teach his brother a lesson Sri Hanuman took form of an old monkey and sat in his way. When Bheem asked Sri Hanuman to remove his tail from his way. Hanuman asked Bheem to do it by himself. Bheem tried to do that but failed in his effort.At that time Sri Hanuman revealed his identity and this way taught a lesson to Bheem.
Pandavas along with Draupadi reach Gandhamadhana mountain. Bhima's son Ghatotkacha and other rakshasas carry them there.
When they were resting, a beautiful 1000 petalled flower falls before Draupadi. She was charmed by its fragrance and effulgence. She asks Bhima to bring many more flowers of that species so that she can take them to her hermitage.
Bhima starts towards North East direction and starts ranging Gandhamadhana mountain range. On his journey he reaches a garden full of fruits. An old ape was lying down in his path. Bhima asks that ape to get up and move away from his path. But that ape refuses to do so. He says he is old and I'll to get up. Since Bhima is strong and healthy man, he asks to move him and continue his journey.
Listening to these words, Bhima was enraged and boasts of his energy. He threatens the old ape to send to abode of Yama (meaning to kill) but he says he was not doing any harm because he belongs to the race of his brother Hanuman. Due to respect towards his brother, he was sparing that ape and not jumping over him to continue his journey. Hearing this statement, ape asks Bhima to move his tail and make a way.
Bhima loses patience. He thought of catch holding tail of that monkey and throwing away. He slightingly catches the tail of that monkey to lift but couldn't move an inch. Then he uses both the hands and finally all of his power. But the long tail didn't move an inch. He prayed to that monkey who he was and begged to reveal his own identity. Thus the pride of Bhimsena was crushed to ground.
That old monkey was none other than Hanuman. He was just acting as an ill ape just to let him know that he was not the strongest.
Hanuman reveals who he was and narrates tale of his birth and the story of Rama. Bhima feels fortunate and extremely happy to meet Hanuman his brother (both are sons of Vayu). Bhima asks Hanuman politely to teach about Yuga Dharma and characteristics of four Yugas. Hanuman being knowledgeable in shastras teaches him. Bhima requests Hanuman to show the original form which he had during Ramayana.
Upon his request, Hanuman assumes vanara form with huge body. He increases his size upon his will. Bhimasena wondered by the appearance. His hair stood up looking at the splendid appearance of Hanuman. Hanuman stopped at a size because Bhima being a human is not capable of seeing beyond that form.
Hanuman due to fraternity gives an opportunity to ask for a boon. Bhima requests his assistance and support in the upcoming war to the Pandavas.
From Chapter 150, (Translation by Kisari Mohan Ganguli)
"Hearing those words of that high-souled one, Bhimasena with a cheerful heart answered Hanuman, saying, 'O foremost of monkeys, I take all this as already performed by thee. Good happen to thee. O mighty-armed one! I ask of thee this,--be thou well pleased with me. O powerful one, on thy having become our protector, the Pandavas have found help. Even by thy prowess shall we conquer all foes." Thus addressed, Hanuman said unto Bhimasena, 'From fraternal feeling and affection, I will do good unto thee, by diving into the army of thy foes copiously furnished with arrows and javelins. And, O highly powerful one, O hero, when thou shall give leonine roars, then shall I with my own, add force to shouts. Remaining on the flagstaff of Arjuna's car will I emit fierce shouts that will damp the energy of thy foes. Thereby ye will slay them easily.'
After saying this, Hanuman vanished from that spot.