Is it obligatory to feed ten poor persons, or is it permissible to feed one poor person ten times, as an expiation for an oath?

"It is not sufficient to feed the same poor person repeatedly for atonement. Rather, the number of poor persons specified by Islamic law must be observed. For instance, the atonement for an oath (kaffarat al-yameen) is not fulfilled by feeding fewer than ten poor persons, and the atonement for ẓihār (a form of divorce) or sexual intercourse during Ramadan is not fulfilled by feeding fewer than sixty poor persons. This is because the legal text has specified this number, and whoever feeds fewer than that has not complied with the command."