Musnad Ahmad 30:2462

Ahmad ibn Abd al-Malik—who is al-Harrani—narrated to us, he said: Zuhayr narrated to us, he said: Ubayd Allah ibn Umar narrated to us, he said: Sa’id ibn Abi Sa’id narrated to me, from his father, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you goes to his bed," and then he mentioned the hadith.