Leviticus 18:21

למלך [AND THOU SHALT NOT LET ANY OF THY SEED PASS THROUGH THE FIRE] TO MOLECH — This was an idol the name of which was "Molech", and this was the manner in which it was worshipped: that he (the father) handed his child (lit., his son, but it applies to his daughter also; cf. Deuteronomy 18:10) over to the priests of the idol. These lit two large pyres one opposite the other and made the child to pass on foot between the two pyres (Sanhedrin 64b). לא תתן refers to “the handing over of the child” to the priests. להעביר למלך — this refers to the “passing through the fire".

וּמִֽזַּרְעֲךָ֥ לֹא־תִתֵּ֖ן לְהַעֲבִ֣יר לַמֹּ֑לֶךְ וְלֹ֧א תְחַלֵּ֛ל אֶת־שֵׁ֥ם אֱלֹהֶ֖יךָ אֲנִ֥י יְהֹוָֽה׃

And thou shalt not let any of thy seed pass through (the fire) to Molekh, neither shalt thou profane the name of thy God: I am the Lord.