Musannaf Ibn Abi Shaybah 32886 — A man who makes a bequest and says

Jarir narrated from Mughirah, and he said that in his opinion Mughirah reported this from Ibrahim, that he said, regarding a man who sealed his will and says to people, "Bear witness to what is written in it!": This is not permissible unless he reads that will out to them, or the will is read out in that man's presence and he acknowledges what is written.