Musannaf Ibn Abi Shayba 16:587

Abu Bakr narrated to us, he said: Jarir narrated to us, from Abu Shayban, from Abdullah ibn al-Hudhayl, who said: Abu Bakr asked the Messenger of Allah (may Allah bless him and grant him peace) about the position of the lower garment (izar). He said: "The middle of the shin. There is no good in what is below that, and there is no good in what is above that."