Musannaf Ibn Abi Shayba 1:1397

Abu Bakr narrated to us, he said: Abd al-Salam ibn Harb narrated to us, from Yazid al-Dalani, from Qatadah, from Abu al-Aliyah, from Ibn Abbas, that the Prophet (ﷺ) said: "There is no ablution required for one who sleeps while prostrating, until he lies down. For when he lies down, his joints relax."