Musannaf Ibn Abi Shayba 20:16

Abu Bakr narrated to us, he said: Yazid bin Harun narrated to us, he said: Muhammad bin Ishaq informed us, from Abu Malik bin Tha'labah, from his father, Tha'labah bin Abi Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) decreed regarding Mahzur, the valley of Banu Qurayzah, that the water should be held back up to the ankles. The upper [land] should not hold back [water] from the lower [land].