Condition to Pay Guarantee from Tithe Funds

A yeshiva student was asked to sign as a guarantor, and he was concerned that the borrower might not pay. Therefore, he stated that his condition was that if he had to pay, he would pay from his tithe funds. In reality, this is what happened; the borrower has no means to pay, and now the guarantor is being asked to pay. The question now is whether the condition is valid, allowing him to pay from the tithe, or if, since he is a guarantor, the debt is considered his, and he cannot pay his debt from the tithe?

Shalom Rav

Since he stipulated in advance that he is signing under this condition, if the borrower is poor to the extent that he is eligible to receive from the tithe, he can pay the guarantee from the tithe funds.