Yahya related to me from Malik from Nafi that Abdullah ibn Umarsaid, "Whoever swears by Allah and then says, 'Allah willing' and thendoes not do what he has sworn to, has not broken his oath."Malik said, "The best I have heard on this reservation is that itbelongs to the statement made if the speaker does not break the normalflow of speech before he is silent. If he is silent and breaks theflow of speech, he has no exception."Yahya said, "Malik saidthat a man who said that he had disbelieved or associated somethingwith Allah and then he broke his oath, had no kaffara, and he was nota disbeliever or one who associated something with Allah unless hisheart concealed something of either of those. He should askforgiveness of Allah and not return to it - for what he did was evil."
USC-MSA web (English) reference: Book 22, Hadith 10
Arabic reference: Book 22, Hadith 1022