Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
ibnmajah:2106ʿAbdullāh b. Muḥammad al-Zuhrī > Sufyān b. ʿUyaynah > Ayyūb > Nāfiʿ > Ibn ʿUmar Riwāyah

"Whoever swears an oath and says In sha' Allah, will never break his oath."  

ابن ماجة:٢١٠٦حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ الزُّهْرِيُّ حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ عَنْ أَيُّوبَ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ رِوَايَةً قَالَ

مَنْ حَلَفَ وَاسْتَثْنَى فَلَمْ يَحْنَثْ