Exodus 21:9

ואם לבנו יעדנה AND IF HE HATH BETROTHED HER TO HIS SON — “He” means the master (not like “he” in the previous verse where it refers both to the master and to the father). The verse teaches you that the son also may succeed to his father’s rights to betroth her to himself, if his father consents to it. Then it is not necessary for him either (just as is not obligatory for his father; cf. v. 8) to perform another act of betrothal, but he merely says to her: “You are designated for me as my wife by means of the money which your father has received from my father as your price” (Kiddushin 19a). כמשפט הבנות [HE SHALL DO UNTO HER] AFTER THE MANNER OF DAUGHTERS — who may claim food, clothing and marital duty (Mekhilta).

וְאִם־לִבְנ֖וֹ יִֽיעָדֶ֑נָּה כְּמִשְׁפַּ֥ט הַבָּנ֖וֹת יַעֲשֶׂה־לָּֽהּ׃

And if he designated her for his son, he shall deal with her after the manner of daughters.