Bava Batra

— But, [it may be replied.] 'this', in fact, [implies that Samuel] is not of the same opinion;  [as, however, his] reason there [for dividing  the monthly rent of the bath house is] because [each one of the parties] is in possession  [of a part of that concerning which they are in dispute], so here  also [the reason why the buyer acquires every se'ah as it is measured out to him is] because it is [then] in his possession. R. Huna said in the name of the school of Rab: [If one says that he would sell an object for] an istira,  a hundred ma'ah, [he is entitled to] a hundred ma'ah. [If he says], 'a hundred ma'ah, an istira'.[he is entitled to] an istira. What does this teach us? That the second expression is to be preferred?  Surely Rab has said it once! For Rab said: Had I been there  I would have given all to the owner.  [Why, then, need Rab say it again?]  — [Since] it might have been said that [the reason Rab would have assigned all to the owner of the bath house] was because [he held that the second expression]  was merely explaining [the first],  therefore,  [it was necessary for Rab] to teach us [the case of the istira].