TT #21 · Parashas Toldos · Passuk 26:12
Yitzchak sowed in that land and reaped a hundredfold the same year. Hashem blessed him,
Torah Temimah points to Kesuvos 112a. E-Daf · Sefaria — Kesuvos 112a
TT lemma: מאה שערים.
Our Rabbis taught: In the blessings of the Land of Israel a beit se’ah produces fifty thousand kor; as it is written “And Yitzchak sowed… and found a hundredfold.”
Custom (Bavli — hundredfold yield of the Land)
Under the blessing of the Land, a single se’ah of seed can produce fifty thousand kor; the hundredfold harvest of Yitzchak is the scriptural measure.