Muḥammad b. Sīrīn – Allāh have mercy on him – said:

A man amongst the Companions of the Prophet ﷺ would go three days without finding anything to eat, so he would take some animal skin, roast it and eat that. If he found nothing at all, he would tie a rock to himself to straighten his back.

Al-Mundhirī, Al-Tarġīb wa Al-Tarhīb. Graded ḥasan by Al-Albānī. See Ṣaḥīḥ Al-Tarġīb wa Al-Tarhīb article 3310.