Midrasch zu Dewarim 9:18

1. "And I besought the Lord" (Deuteronomy 3:23). Halacha: A Jew who stands and prays [the Amidah prayer], may he pray out loud? The sages teach: (Talmud Berachot 31a) "Someone who stands and prays [the Amidah prayer] should hear his own voice [but others should not]. Chanah already explained: (I Samuel 1:13) "And Chanah spoke to herself..." One might think one can pray the three [Amidah prayers throughout the day] as a single [prayer]? Daniel already taught: (Daniel 6:11) "And three times a day he would kneel on his knees, and he would pray and bow before his God." One might think that one should pray at every moment one fancies? David already explained: (Psalms 55:18) "Evening, morning and afternoon I speak and moan, and He hearkened to my voice."

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R. Simlai expounded: "A man should always arrange the praises of the Holy One, praised be He! and then pray for what he needs. Whence do we derive this? From Moses; for it is written (Deu. 3, 23.) And I besought the Lord at that time. And it is written also (Ib.) Thou hast begun to show Thy servant thy greatness, and Thy mighty hand; for what God is there in the heavens or on earth that can do aright like Thy works, and like Thy mighty deeds? And following this it is written Let me go over, I pray Thee, that I may see the good land, etc."