\|/Doubts & Discussions about Lord Shiva Part-1\|/ (Page 141)

Brihaspati (the preceptor of the gods) had an attendant by the name of Punjikasthala who was cursed to assume the body of a female monkey. The curse was to be removed on her giving birth to an incarnation of Lord Siva. Accordingly, she was born as Anjana and, together with her husband Kesari (so named on account of his being as brave as a lion), lived a life of chastity and purity. She performed intense Tapasya (austerities) for a great many years, during which period she worshipped Lord Siva who being pleased with her granted her a boon. She asked that He (Lord Siva) be born to her so that she may be freed from the curse.

When Dasaratha, the king of Ayodhya was given the sacred payasa (pudding) by Agnideva to share among his wives so that they may have divine children (Ram, Lakshmana, Bharata and Shatrughna), by divine ordinance, a bird (kite) snatched a fragment of that pudding and, whilst flying over the forest, dropped it where Anjana was engaged in worship. Pavandev (the deity presiding over the wind) delivered that fragment of pudding to the outstretched hands of Anjana who immediately swallowed it. With that grace, she, in due course, gave birth to Hanumanji. Thus we find that Lord Siva incarnated as Hanumanji in the bodily form of a monkey through the grace and blessings of his god-father Pavandev, with Anjana and Kesari as his earthly parents.

From Vayu puran,