In the Valmiki Ramayan
[Kishkindha kanda (Chapter), sarga (Verse) 66],
the story of Hanuman’s birth is narrated as follows
Hanuman was born to Anjani on parvatithi (An auspicious day). Soon after His birth, Hanuman advanced towards the rising sun as He thought it to be some ripe fruit. That day Rahu (a demon) was present in the sky to devour the sun. Thinking that Hanuman was another Rahu advancing towards the Sun, Indra hurled His vajra (Divine thunderbolt) at Him. The weapon struck Hanuman on His chin and pierced through it. This begot Him His Name, Hanuman. (Hanu means chin). Just like the queens of King Dasharath, Anjani too had performed a vowed religious observance (Vrat) and had received the payas (A sweet delicacy which was given holy sacrament). This is how Hanuman was born to her on the full moon day (Pournima) of the Hindu lunar month of Chaitra. This day is celebrated as ‘Hanuman jayanti’. Hanuman is also known as Hanumant. In the Mahabharat, He is referred to as Marutatmaj. Hanuman has been derived from the word ‘marut’.