Musannaf Ibn Abi Shaybah

Ibrahim says that if someone swears an oath like this: "On the day I do such-and-such work, I will be in the state of ihram for Hajj," then when he breaks his oath, he will become a muhrim (one in ihram). And if he swears an oath like this: "If I do such-and-such work, I will be in the state of ihram for Hajj," and the month of Shawwal has already begun, then he will be considered a muhrim.