Reference for Bava Metzia 134:5
מאן דאסר בקמייתא שרי בבתרייתא מאן דאסר בבתרייתא היכי שרי למיכל שרי כי משכנתא דסורא דכתבי בה הכי במשלם שניא אילין תיפוק ארעא דא בלא כסף
Now, this is well on the view that a stipulated time limit is permitted; but on the view that it is forbidden, what can you say? For it has been stated: As for a stipulated time limit, R. Aha and Rabina differ therein: one maintained that it is permitted — the other that it is forbidden. What is meant by a 'stipulated time limit'? — If he [the creditor said], 'For the first five years, the usufruct is mine without deduction; thereafter, I will make you a full allowance for the crops.' Others maintain: Any arrangement involving no deduction is forbidden. What then is meant by a 'stipulated time limit'? — If he [the creditor] said to him, 'For the first five years the usufruct is mine at a [fixed] deduction;<span class="x" onmousemove="('comment',' Less than the average value of the crops. ');"><sup>5</sup></span>