Musannaf Ibn Abi Shayba 16:609

Abu Bakr narrated to us, he said: Isa ibn Yunus narrated to us, from al-Awza’i, from ‘Amr ibn Muhajir, who said: The shirt of ‘Umar ibn ‘Abd al-‘Aziz and his outer garments (jubab) were between the ankle and the sandal strap.