Peah, Chapter 3, Mishnah 7. The previous Mishnah presented the view of Rabbi Akiva, that even a piece of land of any size at all - the smallest quantity of land - is obligated in Peah. From there the Mishnah continues and deals with additional matters in which land of any size at all determines the halachah.
Introduction: the law of a gift given by a shechiv mera:
A shechiv mera is a person who is on his deathbed. The rule is that when a person distributes his property on his deathbed and gives away all that he owns to particular people during his lifetime, his intention is that the gift take effect before his death. Therefore, if he recovers, everything he gave returns to him, since he gave it only on the assumption that he was about to die and would no longer have any need for his property.
But if he kept something back for himself and gave away only part of his property, he thereby reveals that his giving does not stem from the assumption that he is about to die; rather, it is a complete gift. For that reason, even if he recovers, he cannot retract what he gave. This is the subject of our Mishnah.
The text of the Mishnah:
"HaKosev nechasav shechiv mera, shiyer karka kol shehu - matnaso matanah" - a person who signs over all his property while he is a shechiv mera, and keeps back for himself even the smallest amount of land and does not give it away, even though he cannot take it with him - his gift stands. Even if he recovers and does not die, he cannot take back what he gave, for he kept something for himself, and this shows that his giving had the status of a gift given by a healthy person, like a healthy man who gives a gift.
"Lo shiyer karka kol shehu - ein matnaso matanah" - he kept nothing back for himself but gave everything away, and if he recovered from his illness, his gifts are not considered gifts, and they return to him.
One who signs his property over to his sons, and the wife's kesubah:
The Mishnah brings a further halachah in which land of any size at all is decisive: "HaKosev nechasav levanav" - a man who distributes his property to his sons during his lifetime, instead of leaving it to them as an inheritance after his death. Some explain that this refers to a shechiv mera, and some explain that it applies even to a healthy person who did so during his lifetime.
"Vechasav le'ishto karka kol shehu - ibdah kesubasah" - he included his wife together with the sons and gave her even a tiny amount of land. If she does not protest and says nothing other than expressing agreement, she has lost her kesubah, for it is understood from this that in distributing his property during his lifetime he is treating her as one of the sons, giving each one a portion that takes effect in his lifetime. And since she says nothing, she has agreed to accept her status as one of the sons in place of the kesubah due to her.
"Rabbi Yosei omer: im kiblah aleha, af al pi shelo kasav lah - ibdah kesubasah" - Rabbi Yosei goes even further: it is enough that she accepted it verbally, and even though he wrote nothing over to her at all, she has lost her kesubah under these circumstances.
In summary: this Mishnah continues the discussion of the power of land of any size at all. In the law of a shechiv mera, keeping back land of any size at all proves that the gift has the status of a gift given by a healthy person and does not revert, whereas one who gives everything away without keeping anything back, if he recovers from his illness his gifts return to him. And in the law of one who signs his property over to his sons, writing over land of any size at all to his wife, when she remains silent, places her as one of the sons and causes her to lose her kesubah, and in the view of Rabbi Yosei her verbal acceptance suffices even without any writing.