“The Lord spoke to Moses and to Aaron, saying” (Numbers 2:1). “The Lord spoke to Moses and to Aaron, saying.” In eighteen places you find Moses and Aaron as equals, corresponding to the eighteen blessings. The three patriarchs, from there you find a fixed obligation that one prays three times daily.
Abraham instituted the morning prayer, as it is stated: “Abraham arose early in the morning [to the place where he had stood before the Lord]” (Genesis 19:27). Standing is nothing other than prayer, as it is stated: “Pinḥas stood and prayed” (Psalms 106:30). Isaac instituted the afternoon prayer, as it is stated: “Isaac went out to stroll [lasuaḥ]” (Genesis 24:63). Siḥa is nothing other than prayer, as it is stated: “The prayer of a poor man when he is faint [and pours out his plea [siḥo] before the Lord]” (Psalms 102:1).
Jacob instituted the evening prayer, as it is stated: “He encountered [vayifga] the place…” (Genesis 28:11). Pegia is nothing other than prayer, as it is stated: “And you, do not pray on behalf of this people…[and do not plead [tifga] with Me]” (Jeremiah 7:16). In eighteen places Moses and Aaron are paired. An allusion to the eighteen blessings; they correspond to the eighteen mentions of God’s name that are written in Shema Yisrael and in: “A psalm by David.
Give to the Lord, sons of the mighty” (Psalms 29:1). The three patriarchs instituted that one prays three times daily, and Moses and Aaron [are paired in eighteen places], and from these eighteen mentions of God’s name we derived eighteen blessings.