Halakhah zu Mischlej 3:2

Ramban, may his memory be blessed, also wrote that when the father gives the money to the priest he should first give the child into the priest's hand, and the priest should say, "Which is more beloved to you, your son or these five sela?" And the father responds, "My son is more beloved to me." The priest immediately takes the silver coins and passes them over the head of the son and says, "This is in the place of this, traded for this, this is rendered no longer sacred through this. This goes out to the priest and this child should come to life and Torah and fear of heaven. May it be His will that as this one came to redemption, may he also come to Torah, marriage and good deeds, and let us say amen." The priest places his hands on the son's head and blesses him, according to how he knows to bless him, such as "May the Lord guard you, etc." (Psalms 121:5), or "As length of days and years of life, etc." (Proverbs 3:2) or "The Lord shall protect you from all evil and guard your soul, etc." (Psalms 121:7). And [the father] takes him out for all of his will. [This] and the rest of its details are elucidated in Tractate Bekhorot (see Tur, Yoreh Deah 308).