Midrasch zu Wajikra 25:16

10) (Vayikra 25:15) ("According to the number of years after the Yovel shall you buy from your fellow; according to the number of years of the crops shall he sell to you.") Whence is it derived that one who sells his field when Yovel is in force may not redeem it before two years have passed? From "years ("years" = a minimum of two) shall you buy from your fellow." "after the Yovel": close to the Yovel (that has passed). Whence do I derive (the same for) far from the Yovel? From (Vayikra 25:16) "According to the numerousness of years (until the next Yovel) shall you increase its price and according to the fewness of the years shall you diminish its price." "the years of the crops": A year of wind-blast or yellowing or shevi'ith do not enter into the (two-year) count. If he (the buyer) plowed it (for a season) or let it lie fallow (for a season), it does enter into the count. R. Eliezer says: If he sold it to him before Rosh Hashanah and it was full of fruit, I might think that he (the seller) could tell him: Hand it over to me full, as I handed it to you; it is, therefore, written "according to the number of the years of the crops shall he sell to you" — Sometimes you eat three yields in two years (as in the above instance).