Zevachim Chapter 13, Mishnah 4. This Mishnah too deals with a dispute between Admon and the Sages, this time regarding the law of 'modeh b'miktzas': in what circumstances is a defendant's admission considered an admission to part of the claim, which obligates him to take an oath.
The law of modeh b'miktzas:
When a person makes a monetary claim against his fellow, and the defendant admits to part of it - for example, the claimant says, "You owe me one hundred dollars," and the defendant answers, "True, but I owe you only fifty dollars" - this is a case of 'modeh b'miktzas'. The Torah's law is that he must take an oath in order to be exempt from paying the remainder, that is, he swears that he owes no more than fifty dollars.
However, this obligation applies only when the claim and the admission are for the same type of item - both in money, and both of the same kind. But if a person claimed, "You owe me a se'ah of wheat," and the other replied, "I owe you nothing but half a se'ah of barley" - even though he admitted to half, this is not an admission of the same kind as the claim, and therefore there is no obligation to take an oath at all.
The question of the Mishnah:
The question the Mishnah raises is whether, in a particular case, the original claim includes within it the item to which the defendant admitted, so that it would be considered an admission to part of the claim, or whether that item was never included in the claim to begin with.
"To'ano chaveiro kadei shemen v'hodah b'kankanim" - a person claims that his fellow owes him jugs of oil, and the other admits and says, "Indeed I owe you, but I owe you only the empty jugs, and not the oil inside them."
"Admon omer: hoil v'hodah b'miktzas hata'anah - yishava" - in Admon's opinion, the claim was for both the oil and the jugs, so the defendant has admitted to part of the claim, and therefore the oath of modeh b'miktzas applies to him.
"Vachachamim omrim: ein zo hoda'ah mimin hata'anah" - in the opinion of the Sages, there was no claim regarding the jugs at all. When he said, "You owe me jugs of oil," he meant the oil alone, in the quantity of a jug's worth, and not the jugs themselves. It emerges that his admission is not of the same kind as the claim, and there is no obligation to take an oath.
On this the Mishnah concludes: "Amar Rabban Gamliel: ro'eh ani es divrei Admon" - that is, he accepts the words of Admon, that this admission is considered an admission to part of the claim, and the defendant must take an oath.
In summary: In this Mishnah we learned the fundamental law of modeh b'miktzas, which obligates an oath only when the admission is of the same kind as the claim. In the case of one who claims jugs of oil and the defendant admits only to the jugs, Admon and the Sages disagree as to whether the jugs were included in the original claim, and Rabban Gamliel ruled in accordance with Admon.