From Sahih Bukhari (Hadith 6844):
Narrated `Aisha:Abu Bakr came to me while Allah's Messenger (ﷺ) was sleeping with his head on my thigh. Abu Bakr said (to me), "You have detained Allah's Messenger (ﷺ) and the people, and there is no water in this place." So he admonished me and struck my flanks with his hand, and nothing could stop me from moving except the reclining of Allah's Messenger (ﷺ) (on my thigh), and then Allah revealed the Divine Verse of Tayammum
Reference: Bukhari 6844