R. Eliezer [T2 or T5] says: repayment may be made from one kind for that of another, provided that it is from a superior for that of an inferior kind. R. Akiba [T3] says: repayment can be made only from the same kind. Hence if a man ate cucumbers grown a year before the Seventh Year, he must wait for those grown after the termination of the Seventh Year and repay with them. The same source which causes R. Eliezer [T2 or T5] to be lenient causes R. Akiba [T3] to adopt a stringent ruling; for it is written: and he shall give unto the priest the holy thing, [implying,] whatever is liable to become `holy`. So. R Eliezer [T2 or T5]. But R. Akiba [T3] says: `and he shall give unto the priest the holy thing`, [meaning] the same kind of holy thing which he had eaten.
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