It is narrated from Hazrat Aisha (may Allah be pleased with her) that sometimes the Prophet (peace and blessings be upon him) would be in a state requiring ghusl (ritual bath) in the morning. The Prophet (peace and blessings be upon him) would come to the tub, perform ghusl from it, and then would also observe the fast.
Hadith Referenceمسند احمد / مسند النساء / 25368
Hadith Gradingحکم دارالسلام:حديث صحيح وهذا إسناد مختلف فيه، خ: 1930، م: 1109