Rashi on I Samuel
And I have dedicated him to Adonoy. Just as a person who lends a utensil to his master, or lends him his son to serve him.
Metzudat David on I Samuel
And also: Meaning to say, also at the time of the prayer, I then vowed to lend him to the Lord, to always dedicate himself to His service.
Radak on I Samuel
I lent him: I returned the loan to Him that He gave me. And Yonatan translated it [in the Targum] as, "I gave him over, that he should serve before the Lord."