Musannaf Ibn Abi Shaybah 32854 — A man who makes a bequest and then

Hisham narrated that Muhammad said: People used to make their wills in this way: a man would write in his will, "If death comes to me before I change this will of mine." If he then felt the need to change it, he could change it, whether it was a bequest of freeing a slave or anything else. And if he had not set any such condition in the will, he could still change the will, except for the freeing of a slave.