In the Kishkindha Kanda of the Valmiki Ramayana, the monkey army reaches the sea. Someone must leap across to Lanka. The old Jambavan turns to Hanuman, tells him of his birth and his strength, and says: Uttishtha harishardula, langhayasva maharnavam. Rise, tiger among monkeys, leap across the great ocean. He adds that the whole monkey army wishes to see his strength.
Only then does Hanuman enlarge his body. Valmiki describes him as jambavata prachoditah, urged on by Jambavan.