Ikrimah (may Allah have mercy on him) narrates as marfu' that he (peace and blessings be upon him) said: "By Allah, I will surely make an expedition against Quraysh." Then he said: "In sha' Allah." Then he said: "By Allah, I will surely make an expedition against Quraysh, in sha' Allah." Then he said: "By Allah, I will surely make an expedition against Quraysh." Then he remained silent, then said: "In sha' Allah."
The Shaykh said: It is possible — if this is authentic — that he (peace and blessings be upon him) did not intend to attach the exception to the oath, but said it only because of Allah's words: "And never say of anything, 'I will do that tomorrow,' except (with the words), 'If Allah wills'" [Surah al-Kahf: 23-24].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19930