Lady Aisha Siddiqa (may Allah be pleased with her) narrates: A man came to the service of the Prophet Muhammad (peace be upon him). He said: O Messenger of Allah (peace be upon him)! Sometimes I am in a state of janabah (major ritual impurity) at the time of true dawn (Fajr), so should I fast that day? I heard the Prophet Muhammad (peace be upon him) say: Sometimes I am also in a state of janabah at the time of true dawn, but I get up, perform ghusl (ritual bath), offer the morning prayer, and I also fast that day. The man said: You are not like us. Allah Almighty has forgiven your past and future sins. So the Prophet Muhammad (peace be upon him) said: I hope that I am the most God-fearing among you and the most knowledgeable among you regarding what leads to piety.
(Imam Ibn Hibban, may Allah have mercy on him, says:): The statement of the Prophet Muhammad (peace be upon him), "I hope," contains evidence that a person may verbally express hope regarding something about which he has no doubt. It also contains evidence that making an exception in an oath in this manner is permissible, as we have mentioned at the beginning of the book.