Commento su Esodo 17:11

כאשר ירים משה ידו WHEN MOSES LIFTED UP HIS HAND — But could Moses’ hands win the battle etc.? See the whole passage as it is given in the Treatise Rosh Hashanah 29a.

AND WHEN HE LET DOWN HIS HAND, AMALEK PREVAILED. By way of the plain meaning of Scripture, when Moses was compelled to lower his hands because of weariness, he saw that Amalek prevailed. He then commanded Aaron and Hur to support them, and thus he would not lower them again. Our Rabbis have said in the Midrash:⁴⁶³Sefer Habahir, 138. “Did Moses cause Amalek to prevail over Israel? It was merely because a person is forbidden to tarry three hours with his hands spread heavenward.”⁴⁶⁴See my Hebrew commentary for a quote from the Cabalistic work of the Tziyoni for an explanation of this doctrine. In his commentary on the Sefer Habahir (p. 61, Note 4), Reuben Margoliot quotes from the Commentary of the Vilna Gaon on Proverbs (25:17) that “one must not pray [any given Service] more than three hours.”

כאשר ירים משה ידו, and his staff.