Sunan Abi Dawud

Narrated Abdullah ibn Umar: When the Prophet (ﷺ) wanted to relieve himself, he would not raise his garment, until he lowered himself near the ground. Abu DAwud said: This tradition has been transmitted by 'Abd al-Salam b. Harb on the authority of al-A'mash from Anas b. Malik. This chain of narrators is weak (because A'mash's hearing tradition from Anas b. Malik is not established)