Sanhedrin Chapter 7, Mishnah 7. The Mishnah continues to explain some of the commandments mentioned earlier in Mishnah 4, the violation of which can incur stoning, and discusses three of them.
One who gives his offspring to Molech:
According to the Gemara's approach to our Mishnah, this ritual is indeed a religious one, but it is not a form of worship of the idol Molech; rather, it is a Canaanite custom. This is similar to how one does not say about taking a lulav or performing a bris milah that they are "worship" of God - they are Jewish ritual acts, but not worship per se. The same applies here: it was a Canaanite custom to pass some of a person's children to the idol Molech in some manner.
This process has two stages: first, handing the child over to the kohen of Molech, and then the kohen returns the child to the parent, and the parent carries him over the fire. Two separate verses deal with this, each from a different angle - one regarding the handing over and the other regarding the passing through fire - and from this the Mishnah learns that both components are required to incur stoning:
"Umi'zaracha lo sitein l'haavir lamolech" (Leviticus 18:21) - You shall not hand over any of your children to pass them to Molech. This is the handing-over stage.
"Lo yimatzei b'cha maavir b'no u'vito ba'eish" (Deuteronomy 18:10) - There shall not be found among you anyone who passes his son or his daughter through the fire. This is the stage of passing through the fire.
And so reads the Mishnah: "Hanosein mizaro lamolech eino chayav" - One who gives his offspring to Molech is not liable to stoning (putting aside for now the laws of testimony and warning), "ad she'yimsar lamolech v'yaavir ba'eish" - until he hands the child over to the kohen and then passes him through the fire. "Masar lamolech v'lo he'evir ba'eish, he'evir ba'eish v'lo masar lamolech - eino chayav" - If he handed over to Molech and did not pass through the fire, or passed through the fire and did not hand over to Molech, he is not liable. In some versions, the continuation of the text "ad she'yimsar lamolech v'yaavir ba'eish" is omitted, as it is indeed redundant.
Baal Ov and Yidoni:
The second part of the Mishnah, which appears in the Talmud Bavli as an independent Mishnah, discusses two other commandments mentioned in Mishnah 4 that are related to each other: a baal ov and a yidoni. These are two different forms of raising spirits, consulting with the dead to foresee the future. The Mishnah establishes that one who performs either of these two acts of sorcery can incur stoning, while one who consults them violates a regular negative prohibition and only receives lashes.
"Baal ov" - This is one who performs the ov ritual, and speaks from his armpit. According to the Bartenura, and also according to the Rambam, there is a skull here that serves as the source consulted: they burn incense toward it and ask it questions, and then a voice is heard - either from the armpit of the baal ov (the person asking and burning the incense), as the Mishnah explicitly states, or from the earth, seemingly from under the ground in a very faint voice. The Rash seems to understand that this refers to only one thing, the armpit, and not two.
"Yidoni" - One who speaks from his mouth. The Gemara explains that there is an animal called yidoa, and this involves a bone from this animal. The sorcerer places the bone into his mouth, directs the questions to the dead, and the voice comes out of his mouth - from that bone in his mouth.
Although the verse forbids ov and yidoni together, we learn that each of them is a separate transgression and one is liable for each one independently, because another verse says not to turn to the ovos - this is one type, and then there is the second type. They are two separate things.
Both of these refer to those who perform the act, and those who perform it are liable to stoning. However, one who consults them - his punishment is lashes. It is fitting to ask: King Saul consulted a female medium (baalas ov), so how was this permitted for him? The answer is that it was not permitted, but Saul believed he was obligated to do so as a way to save his soldiers.