Ketubot 203
דאמר רב גידל אמר רב כמה אתה נותן לבנך כך וכך וכמה אתה נותן לבתך כך וכך עמדו וקידשו קנו הן הן הדברים הנקנין באמירה
since R. Gidel has said in the name of Rav: [If one man said to another], “How much are you giving to your son?” [and the other replies] “Such and such a sum,” and [the other said,] “How much are you giving to your daughter?” [and the other replies], “Such and such a sum,” if they betroth, they have performed kinyan (acquisition), and these are the things which are acquired by verbal agreement.
אי הכי בנו אמאי אינו פדוי כדעולא דאמר עולא דבר תורה פדוי לכשיתן ומ"ט אמרו בנו אינו פדוי גזירה שמא יאמרו פודין בשטרות
If that is the case why is not his son redeemed? This accords with Ulla; For Ulla said: According to the Torah, [the son] is redeemed as soon as [the father] gives the money. And why then did they say that he was not redeemed? It is a decree lest they say that redemption can be done with documents.
אמר רבא כתנאי ערב היוצא אחר חיתום שטרות גובה מנכסים בני חורין
Rava said: This is like the dispute of Tannaim: [If the guarantee] of a guarantor appears below the signing of the document, [the creditor] may recover his debt from unencumbered property.
מעשה בא לפני רבי ישמעאל ואמר גובה מנכסים בני חורין אמר לו בן ננס אינו גובה לא מנכסים בני חורין ולא מנכסים משועבדים
Such a case once came before R. Ishmael and he said that [the debt] may be recovered from unencumbered property. Ben Nannas said to him: He may not collect either from unencumbered property or from property with a lien on it.
אמר לו למה אמר לו הרי שהיה חונק את חבירו בשוק ומצא חבירו ואמר לו הנח לו ואני אתן לך פטור שלא על אמונתו הלוהו
He said to him: Why? He said back: Behold if one was choking another in the street, and his friend found him and said to him, “Leave him alone and I will pay you,” [where he is undoubtedly] exempt from liability, since the loan was not made through trust in him.”