Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) conveyed from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "Whoever swears an oath and says 'In sha' Allah' (if Allah wills) has made an exception."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19914
Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever swears and says 'In sha' Allah' (if Allah wills) has an exception." This is how I found it.
This hadith is known as marfu' only through the narration of Ayyub al-Sakhtiyani.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19915
Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "Whoever swears an oath about something and says 'In sha' Allah' (if Allah wills) has the choice: if he wishes he may fulfil the oath, or he may leave it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19916
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever makes an exception in his oath has the choice: if he wishes to fulfil his oath, he may do so; otherwise there is no harm in leaving it either."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19917
Ibn Ulayyah also mentioned it similarly, except that there is doubt in its transmission from Ayyub; at its end it says: "He may go back on it without being in breach of his oath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19918
Hammad bin Zayd said: Ayyub used to narrate this hadith as marfu' (from the Prophet (peace and blessings be upon him)), then he stopped doing so.
The Shaykh said: Perhaps he stopped only because of a doubt that came to him about its being marfu'. He is Ayyub bin Abi Tamimah al-Sakhtiyani. It has also been narrated from Musa bin Uqbah, Abdullah bin Umar, Hassan bin Atiyyah and Kathir bin Farqad, from Nafi', from Ibn Umar (may Allah be pleased with them both), from the Prophet (peace and blessings be upon him), but its being marfu' is hardly sound except through Ayyub al-Sakhtiyani, and Ayyub too had doubt about it. The narration of the group through sound routes from Nafi', from Ibn Umar (may Allah be pleased with them both), is his own statement, not marfu'. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19919
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: Whoever says "By Allah", then says "In sha' Allah" (if Allah wills), and then does not do what he swore to do, is not in breach of his oath.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19920
Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Whoever swears an oath and says "In sha' Allah" (if Allah wills) has made an exception.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19921
Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "O Mu'adh bin Jabal! When a man says to his wife: 'You are divorced, if Allah wills', she is not divorced; but when he says to his slave: 'You are free, if Allah wills', then he is free."
Only Humayd bin Malik narrated it, and he is majhul (unknown). There is disagreement over its chain from him: it is said as above; it is said: from him, from Makhul, from Malik bin Yukhamir, from Mu'adh; and it is said: from him, from Makhul, from Mu'adh, which is munqati' (broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19923