The hair of the Messenger of Allah ﷺ reached down to the middle of his ears.
كان شعر رسول الله ﷺ إلى أنصاف أذنيه.
No references are available.
Muslim narrated it in the Book of Virtues (96:2338) through several routes from Ismail bin Ulaya, from Humayd, from Anas, who said, and then he mentioned it.