Ibn Abbas (may Allah be pleased with them both) said concerning the expiation of an oath: He has been given the choice among the first three things; if he does not find (them), then it is fasting for three consecutive days.
(b) Ibn Abbas (may Allah be pleased with them both) said: Everything in the Qur'an (stated with) "or" and "or" is a choice; and if he does not find (it), then it is the first, then the next first (in order).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20006