Reference for Bava Kamma 236:4

ומי אמר רב הכי והאמר רב החזירו לעדר שבמדבר יצא אמר רב חנן בר אבא מודה רב ברקועתא

Did not Rab Say: If the thief restored [the stolen sheep] to a herd which the proprietor had in the wilderness, he would thereby have fulfilled his duty!<span class="x" onmousemove="('comment',' Is this ruling not in conflict with the statement made above by Rab? ');">⁶</span> — Said R. Hanan b. Abba: Rab would accept the latter ruling in the case of an easily recognisable lamb.<span class="x" onmousemove="('comment',' Lit., spotted'. I.e., the presence of which is conspicuous, so that the shepherd who was looking after the flock in the wilderness would surely notice its restoration. ');">⁷</span>

Jastrow