Valmiki Ramayana Ayodhya Kanda Sarga 54 Shloka 31

तत्र there, बहवः many, ऋषयः ascetics, शरदां शतम् for hundreds of years, तपसा with austerities, विहृत्य having roamed about, कपालशिरसा सह with the skulls on their heads, दिवम् heaven, आरूढाः have ascended.

On the Chitrakuta mountain many ascetics wandered about (lived) for hundreds of years carrying on penance. In the process they became so much emaciated that they looked as if they were left (only) with the skulls on their heads. (In the end) they ascended heaven.