Reference for Bava Metzia 9:7
ת"ש דתני אבוה דרבי אפטוריקי לדרבי חייא קמייתא מנה לי בידך והלה אומר אין לך בידי כלום והעדים מעידים אותו שיש בידו חמשים זוז יכול ישבע על השאר
Come and hear what the father of R. Apotoriki taught, as a refutation of the first [law of] R. Hiyya: [If one says to another,] 'You have a hundred [<i>zuz</i>] in your possession belonging to me', and the other says, 'I have nothing belonging to you,' and witnesses testify that the defendant owes the plaintiff fifty [<i>zuz</i>] — I might think that the defendant ought to swear regarding the rest; therefore the Scriptural text tells us, for any manner of lost thing, whereof he saith that it is this,<span class="x" onmousemove="('comment',' Ex. XXII, 8. The term 'It is this' is construed as implying a partial admission. V. Shebu. 39b; B. K. 107a. ');"><sup>6</sup></span>