Mishnah Bava Batra 8:6 — Sefaria version 'Mishnah Yomit by Dr. Joshua Kulp' (CC-BY; source: learn.conservativeyeshiva.org) (CC BY)
If a man said, “This is my son”, he is believed. If [he said], “This is my brother”, he is not believed, yet the other may join him in his portion. If he died the property returns to its place. If he inherited property from elsewhere the other’s brothers inherit it together with him. If a man died and a testament was found bound to his thigh, this counts as nothing. But if [he had delivered it and] through it granted title to another, whether of his heirs or of those who are not his heirs, his words are valid.
Reproduced in full. Translation: Sefaria version 'Mishnah Yomit by Dr. Joshua Kulp' (CC-BY; source: learn.conservativeyeshiva.org) (CC BY).
Why Pitre cites it
A man's declared disposition of his property is binding — the legal background Pitre gives for Jesus' will from the cross.
Notes
The mishnah's relevant clause is 'If a man died and a testament was found bound to his thigh, this counts as nothing. But if [he had delivered it and] through it granted title to another ... his words are valid.' The maxim 'the words of a dying man are as though written and delivered' (divrei shekhiv mera ki-khetuvin u-kimsurin damu) is Talmudic, not in this mishnah: see Bavli Bava Batra 151a / 175a and Gittin 13a, 15a (Davidson translation on Sefaria, CC-BY-NC). Davidson/Steinsaltz renders the mishnah's will as 'a will written by a person on his deathbed [dayetikei]'.