Translation:Shulchan Aruch/Choshen Mishpat/21
Paragraph 1- If someone made a kinyan that if he does not come by a certain date and take an oath, then his adversary would be believed on whatever he claims without taking an oath or if he made a kinyan that if he does not come by a certain date to swear and collect, then he has forfeited his rights and his adversary will be exempt and he will get nothing, and the day passed without him showing up, the condition has been fulfilled and he has forfeited his rights. We do not give him any additional time. If he brings proof that something out of his control occurred, he is exempt from complying with this kinyan, and he can swear to respond to his adversary’s claims just as he could earlier. The same applies for anything similar. This is only true where they made an actual kinyan. Otherwise, it does not work because it is merely an asmachta.