According to Hindu scripture Bhavishya Purana, during the war between Gods and demons, Indra – the deity of sky, rains and thunderbolts – received setbacks at the hands of the powerful demon king Bali.
After this defeat, Indra sought the advice of Brihaspati (the Devaguru). On the advice of the Devaguru, Indrani (the consort of Indra) tied silken amulets (Raksha Bandhan), received from lord Vishnu (blessed by him with prayers and success) on Indra’s wrists, on the auspicious occasion of Shravan Poornima. As a result, Indra successfully defeated the evil and recovered Amaravati, his celestial dwelling.
This story inspired the protective power of holy thread.
The story also suggests that the Raksha Bandhan thread in ancient India were amulets, used by women as prayers and to guard men going to war, and that these threads were not limited to sister-brother like relationships.