Reference for Bekhorot 111:17

אמר רבא

I might have said, however, that just as [the rule of] 'thy first-born son' does not apply at all to where he is bought, similarly [the rule of] 'thine oxen and wi thy sheep' does not apply at all to where they are bought; why then did R'Assi report in the name of Rab Johanan: If one bought ten embryos which were in the insides of their mothers they all enter the shed to be tithed?<span class="x" onmousemove="('comment',' Tosaf. observes that the same ruling applies even if they were already born, but are too young for sacrifice.');">⁹</span>

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