Musnad Ahmad Hadith 18888

It is narrated from Ammar bin Yasir (may Allah be pleased with him) that once the Holy Prophet (peace and blessings of Allah be upon him) camped at a place with an army during the last part of the night. The noble wife of the Holy Prophet (peace and blessings of Allah be upon him), Aisha (may Allah be pleased with her), was also with him. That same night, her ivory necklace broke and fell. The people stopped to search for her necklace. This continued until the break of dawn, and the people did not have any water (to perform ablution for prayer). On this occasion, Allah Almighty revealed the concession in ablution, that is, the command to perform tayammum with pure earth. Abu Bakr Siddiq (may Allah be pleased with him) said to his daughter Aisha Siddiqah (may Allah be pleased with her), "By Allah! I did not know that you are so blessed; Allah has revealed a concession upon us because of you." So we struck the earth once for the face and once for the hands up to the shoulders and armpits.