Maulana Mohammad Ali:
Allah will not call you to account for that which is vain in your oaths, but He will call you to account for the making of deliberate oaths; so its expiation is the feeding of ten poor men with the average (food) you feed your families with, or their clothing, or the freeing of a neck. But whoso finds not (means) should fast for three days. This is the expiation of your oaths when you swear. And keep your oaths. Thus does Allah make clear to you his messages that you may give thanks.
Surah Al Maidah (The Table Spread with Food) Ayat 90