Devdutt Pattanaik says this in one of his talks - when Agni wouldn't burn her, Sati burnt herself with her own internal fire, according to him. Is there scriptural basis for this?
The works of Devdutt Pattanaik are not reliable, as they paint the characters from Hindu literature in a wrong manner.
Shiva Purana says that angered with her father Daksha's behaviour towards Shiva, Sati decides to cast off her body, as she was born to Daksha.
Fie upon Him who is always wicked and who perpetrates actions of unspeakable demerit. Sensible man should shun even the contact with such a man.
I am the offspring of your race as the bull-bannered lord Śiva has often said. Hence naturally my name has come to be Dākṣāyaṇī. This is distressing to me.
This body born of your limbs I shall cast off as a corpse. It is worthy of contempt. I shall abandon it and gain happiness.
Later she sats in Yogic posture, meditating on Shiva, reduces her body to ashes.
- Her body divested of its sins fell in the yogic fire and was reduced to ashes, O excellent sage, in accordance with her own wish.
There was no mention of Agni refusing to burn her, in this chapter.