Responsa for Bava Metzia 31:2
סוף סוף קרו ליה בני לוקח גזלנא
But according to the view [of R. Ashi, viz.,] 'he wished to vindicate his honesty,' [it could be applied even to this case], as he [the robber] would wish to vindicate his honesty before [the buyer's] children also. [But, it is argued,] would not the buyer's children call him [who sold the field to their father] a robber?<span class="x" onmousemove="('comment',' Even when the buyer is dead, the desire on the part of the seller to vindicate his honesty may still have been the motive for his action in buying the field from the rightful owner, as the children of the dead buyer would call him a robber when they discover that the field was sold to their father unlawfully, and that they could not retain possession of it. ');"><sup>2</sup></span>
Shut min haShamayim
Teshuvot Maharam
A. If A, B and C had made an agreement that they be partners in all good business transactions that come to the house, C is entitled to his share even though he was not present at the time the article was bought; for, although a person cannot sell to another anything that is not yet in existence, people may enter into a partnership to divide future gains (not yet in existence) as in such a partnership each partner merely becomes a hired worker to work for the benefit of the other partners. But if no such agreement exists, A and B must take an oath that C was not one of the buyers of the article, and that he was not present at the time the transaction took place and did not say: "I want to be a partner to this transaction." If, however, C was present at the time and expressed his desire to be a partner, he is entitled to his share of the profits; for, if one person tells another to lift up for him an article which has no owner, and this person picks it up, the former gains title to it; especially so if the second person is also to gain part ownership in the article, as in the present case.
SOURCES: Pr. 325.