Musnad Ahmad 1243:9

Hajjaj ibn Muhammad narrated to us, he said: Shu'bah narrated to me, from Yahya ibn al-Husayn, he said: I heard my grandmother narrating that she heard the Prophet, peace and blessings of Allah be upon him, at Mina, supplicate for those who shave their heads three times. It was said to him: "And for those who shorten [their hair]?" He said in the third [time]: "And for those who shorten."