Midrasch zu Wajikra 27:17

4) (Vayikra 27:17) "If from the Yovel year he shall consecrate his field, according to your valuation shall it stand." Whence is it derived that one is not permitted to consecrate his field at the time of Yovel and that if he does, it is not consecrated? From "If from the Yovel year he shall consecrate his field." "his field": What is the intent of this (apparent redundancy)? Where is it derived that if there were in it clefts ten tefachim deep or rocks ten tefachim high they are not measured together with it? From "his field."

5) "according to your valuation shall it stand": He gives forty-nine selaim and forty-nine pondionoth. What is the nature (i.e., the purpose) of this pondion? It is the premium (for exchange of currency).