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