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 in the morning where ghusl (ritual bath) was obligatory by choice, and then he would also observe fasting.
Hadith Referenceمسند احمد / مسند النساء / 25501
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد منقطع لأن ابن سيرين لم يسمع من عائشة