One who lends another money with a document collects from mortgaged properties; with witnesses, he collects [only] from available properties. [If] he produced his handwritten [note] that he is indebted to him, he collects [only] from available prop-erties.  [If] a guarantor appears below the document's signatures, he collects [only] from available properties. A case came before R' Yishmael, and he said: He collects [only] from available properties. Ben Nannas said to him: He collects neither from mortgaged properties nor from available properties. He said to him: Why? He said to him: [If] someone was choking someone in the street, and another encountered him and said, “Let him alone,” he is exempt, because he did not lend him due to his trust in him. Rather, which is a guarantor who is liable? [if he said,] “Lend him, and I will give you,” he is liable, because he lent him due to his trust in him. Said R' Yishmael: One who wishes to become wise should involve himself in [the study of] monetary laws, as there is no branch of Torah greater than them, because they are like a welling fountain. And one who wishes to in-volve himself in monetary laws should serve Shimon ben Nannas.