"And the boy grew, and the LORD blessed him" (Judges 13:24). With what did He bless him? Rav Yehudah said that Rav said: He blessed him in his body, that his body was like that of [other] men [in proportion], and his seed flowed like a rushing stream.
How the Lord Blessed the Growing Boy Samson
Yalkut Shimoni on Nach 69:3
ויגדל הנער ויברכהו ה' במה ברכו, א"ר יהודה א"ר ברכו באמתו אמתו כבני אדם וזרעו כנחלל שוטף: