Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "By Allah, I will make an expedition against Quraysh! By Allah, I will make an expedition against Quraysh!" Then he remained silent for a while, then said: "In sha' Allah (if Allah wills)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19927
It is also reported likewise from Sharik (may Allah have mercy on him); he said: Then he remained silent for a while, and then said: "In sha' Allah (if Allah wills)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19928
Ikrimah (may Allah have mercy on him) said that the Prophet (peace and blessings be upon him) said: "By Allah, I will make an expedition against Quraysh! By Allah, I will make an expedition against Quraysh! By Allah, I will make an expedition against Quraysh!" Then he said: "In sha' Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19929
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
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) held that making an exception is valid even if it comes a year later. Then he recited: "And never say of anything, 'I will do that tomorrow,' except (with the words), 'If Allah wills.' And remember your Lord when you forget" [Surah al-Kahf: 23-24], that is, whenever you remember.
Then Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: "Whenever he remembers to make the exception, let him make it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19931