According to CFA, JS says papyri were written by the hand of Abraham.
Charles Francis Adams, Sr., Journal, 15 May 1844; rep. Henry Adams, "Charles Francis Adams Visits the Mormons in 1844," Proceedings of the Massachusetts Historical Society 68 (Oct., 1944 - May, 1947): 285
Upon our return form the meal we were introduced into another chamber with had been prepared in the interval, and here we sat down and held a long conference with the prophet upon himself, his doctrines and his projects. He then took us down into his mother's chamber and showed us four Egyptian mummies stripped and then undertook to explain the contents of a chart or manuscript which he said had been taken from the bosom of one of them. The cool impudence of this imposture amused me very much. "This," said he, "was written by the hand of Abraham and means so and so. If anyone denies it, let him prove the contrary. I say it." Of course, we were too polite to prove the negative, against a man fortified by revelation.