Abu Dawud

Explanation:
1:
According to this hadith, if the one swearing an oath says "in sha Allah" (if Allah wills) along with it, then there will be no expiation (kaffarah) upon breaking such an oath.
This is because when an oath is made conditional upon the will of Allah, that oath does not become binding.
And when the oath is not binding, then the question of expiation upon breaking it does not arise.

Benefits and Issues:
Since all matters are fulfilled by the will (mashiyyah) of Allah, the Mighty and Majestic,
therefore, it is from good etiquette in oaths to say “in sha Allah” (if Allah wills) regarding future matters.
In this way, if the oath-taker is unable to fulfill the action, the oath will not be broken.
However, if the one swearing the oath says “in sha Allah” merely to reassure his listener, while intending in his heart to go against it,
then this is a very great sin.
(Indeed, actions are by intentions)

Benefits and Issues:
➊
In the Noble Qur’an, Allah the Exalted has said:
﴿وَلَا تَقُولَنَّ لِشَيْءٍ إِنِّي فَاعِلٌ ذَٰلِكَ غَدًا ۔ إِلَّا أَن يَشَاءَ اللَّـهُ﴾ ( al-Kahf: 18/23, 24)
“Never say about anything, ‘I will certainly do that tomorrow,’ except (by adding), ‘if Allah wills.’”
Therefore, saying “in sha Allah” is also called making an exception (istithna’).
By this, one expresses reliance upon Allah, that whatever will happen will be by His enabling.

➋
Saying “in sha Allah” along with an oath means: My firm intention is indeed to do such-and-such, but if Allah’s decree is otherwise and some excuse arises for me, then this action will not be possible.

(1) The meaning of "insha Allah" is: if Allah, the Exalted, wills. These words clearly indicate that the one swearing the oath has not made an absolute oath. It is as if he is saying: if I am able to do this, I will do it; otherwise, it will be understood that Allah, the Exalted, did not will it for us, thus this action could not be accomplished. Obviously, how could there be any sin upon this? However, in promises and the like, "insha Allah" should not be used as an excuse for breaking a promise; rather, it should be recited only for the sake of blessing (tabarrukan). Otherwise, the promise would have no value.

(2) The apparent utterance of the words "insha Allah" is intended. If someone says "insha Allah" only in his intention, it will not be considered valid, because the establishment of an oath is proven by outward words, not by intention.

Takhrij:
«أخرجه أبوداود، الأيمان والنذور، باب الاستثناء في اليمين، حديث:3261، والترمذي، النذور والأيمان، حديث:1531، والنسائي، الأيمان والنذور، حديث:3824، وابن ماجه، الكفارات، حديث:2105، 2106، وأحمد:2 /10، وابن حبان (الموارد)، حديث:1183، 1184.»©Explanation:
From this hadith, it is understood that if the one who swears an oath says "in sha Allah" (if Allah wills) along with it, then even if he breaks the oath, he will not be considered as having committed the act of breaking an oath, nor will expiation (kaffarah) become obligatory upon him. This is because when an oath is made conditional upon the will of Allah, then by consensus, that oath does not become binding.