Nafi' reports from Ibn Umar (may Allah be pleased with them both): When a man swears an oath and makes an exception, saying "In sha' Allah" (if Allah wills), joining the exception to his words, and then does what he swore about, he is not in breach of his oath.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19924