May one back out of a loan after giving his word to the borrower?
Legal liability: If one said he would loan money to someone he is not legally liable to go through with the loan and the borrower cannot force him in court to give him the money. If however, an IOU document was already written with the consent of the lender, then some Poskim rule he is liable to give the borrower the money. Other Poskim however rule he can go back from the loan even in such a case.
Breaking a Neder: If one said he would loan money to someone who is in need then although there is no legal liability, it is forbidden to back out of his word due to a Neder, just as is the law regarding charity pledges. If one desires to retract his word he is to perform Hataras Nedarim. If however the person who is borrowing the money is not in need, and is borrowing it for extracurricular matters, then he is not obligated to keep his word, although he is considered untrustworthy [i.e. Mechesareiy Emuna] and the Sages are not happy with him as a person is supposed to keep to his word. Due to the above law, one is to initially state “Beli Neder” upon taking upon himself to give someone a loan.
A pledge to give a loan is not legally binding and can be retracted at any time. Nevertheless, at times making the pledge is considered a Neder and one hence must perform Hataras Nedarim to back out from his word. Likewise, even when the pledge does not have the power of a Neder, it is considered unethical to not fulfill one’s word. As a word of advice, in call cases one is to say Beli Neder when making the pledge in order to avoid the above issues.
 See Ahavas Chesed Mitzvas Halvah 1/11 and Nesiv Hachesed 18
 Michaber C.M. 39/17; Nesiv Hachesed ibid that this applies according to all; See Admur Dinei Mechira 1 “A transaction is not compelted through words”
 Shach 39/49 in name of Ramban and Riy Migash
 Michaber ibid
 The reason: As giving a loan to a person in need is a Biblical command [Admur Halva 1] and if one accepts upon himself to perform a certain Biblical or Rabbinical Mitzvah then it is considered a vow]. [See Y.D. 213/2 [in Michaber regarding learning and in Rama regarding all Mitzvos]; 203/4 and Shach 203/4 regarding charity; M”B O.C. 238/5 [regarding all matters of a Mitzvah]
 Nesiv Hachesed ibid 18
 See Ahavas Chesed ibid; Admur ibid
The reason: As there is no obligation to lend money to a wealthy man for a long period of time [Ahavas Chesed ibid] and the same applies regarding lending for extravagances, that there is no obligation to lend him money. [See next Q&A] Therefore, his word is not considered a Neder, and he can back track from it. Nevertheless, not keeping one’s word would fall under a separate prohibition of “Mechusarei Emuna” as brought in Admur ibid. [Ahavas Chesed ibid]
 M”B ibid