The Gemara says that regarding monetary matters, one may harbor ill (even to a Torah scholar) until he actually returns the money to its rightful owner. Apparently teshuva (repentance) is not suffiecient. How is this consistent with the Gemara in Kiddushin (49b) which states that if one in mekadesh a woman on condition that he is a tzaddik, even if he was a known rasha (presumably having violated interpersonal monetary prohibitions as well) nevertheless the Kiddushin is valid on the chance that he quickly repented in his heart. In our Gemara it seems that simply contemplating thoughts of teshuva is not sufficient regarding monetary matters, unless he substantiates it with proper action.
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