Responsa על קידושין 42:21

R. Hayyim Eliezer exchanged correspondence with R. Mordecai regarding a case wherein A [who was critically ill] gave a bill of divorcement to his wife on condition that should he recover, she would have to remarry him. This bill of divorcement was written at twilight. R. Hayyim Eliezer remarks that he would neither validate nor invalidate this divorce until he hears further from R. Mordecai on this matter.
R. Hayyim Eliezer then writes that when he was visited by R. Levi, the latter filled in the following details, concerning the case:
A, who was critically ill, was instructed [by R. Levi] that he must issue a divorce to his wife effective as of now, without any stipulations whatsoever. A agreed to abide by all the instructions [of R. Levi]. However, A petitioned that his wife should not wed anyone else but should remarry him, upon his recovery.
R. Levi thereupon asked A's wife whether she would agree to A's request, and she replied in the affirmative. R. Levi thereupon asked A whether the latter wanted to issue the divorce, effective as of now, and A agreed. The divorce was issued, and subsequent to the interval needed for an utterance to take effect, A cried out, "If I die, the divorce shall take effect as of now, on condition that my wife would have to remarry me, upon my recovery". Were it not for the fact that R. Levi instructed A to announce "If I die, the divorce should take effect as of now", A would have remained silent, and would not have added the stipulation which required his wife to remarry him upon his recovery.