Bava Batra 352:1

ערב דבית דין הוא דלא בעי קנין הא בעלמא בעי קנין

only [in the case of] a guarantor appointed by a court of law is no <i>kinyan</i> required;<span class="x" onmousemove="('comment',' The reason is given infra. ');">¹</span> in all other cases, however, <i>kinyan</i> is required.

והלכתא ערב בשעת מתן מעות לא בעי קנין אחר מתן מעות בעי קנין ערב דבית דין לא בעי קנין דבההיא הנאה דמהימן ליה גמר ומשעבד ליה:

And the law is: [If one] guarantees [a loan] at the time the money is delivered,<span class="x" onmousemove="('comment',' I.e., when the loan was made. ');">²</span> no <i>kinyan</i> is required;<span class="x" onmousemove="('comment',' Since the loan was obviously made through trust in the guarantor, he assumes full responsibility. ');">³</span>

<br><br><big><strong>הדרן עלך גט פשוט וסליקא לה מסכת בבא בתרא</strong></big><br><br>

if, after the money is delivered, <i>kinyan</i> is required;<span class="x" onmousemove="('comment',' To enable the creditor to recoup himself. ');">⁴</span> [and in the case of] a guarantor appointed by a court of law<span class="x" onmousemove="('comment',' Though after the loan has been made. ');">⁵</span> no <i>kinyan</i> is required, for, having regard to the pleasure he has in the confidence reposed in him,<span class="x" onmousemove="('comment',' Lit., 'that he is trusted' by the court. ');">⁶</span> he [wholeheartedly] determines to shoulder the full responsibility.<span class="x" onmousemove="('comment',' Lit., 'and subjects himself to him', i.e., to the creditor. ');">⁷</span>