Sayyidah Aishah (may Allah be pleased with her) said: the Messenger of Allah (peace and blessings be upon him) woke up and the time of the prayer had come. Water was searched for but it was not found, so the verse of tayammum was revealed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1102