Midrash su Salmi 102:6

And God Almighty give you mercy before the man (Gen. 43:14). May it please our master to teach us the number of times a man must pray each day. Thus did our masters teach us: A man must not pray more than three times each day, as instituted by the patriarchs of the world. Abraham established the morning prayer, as it is said: And Abraham got up early in the morning to the place where he had stood before the Lord (Gen. 19:27). The word stood refers only to prayer, as is said: Then stood up Phinehas, and prayed (Ps. 106:30). Isaac instituted the afternoon prayer, as it is said: And Isaac went out to meditate in the field (Gen. 24:63). The word meditation is used with reference to prayer, as it is said: A prayer of the afflicted when he fainteth, and poureth out his meditation for the Lord (Ps. 102:6). Jacob introduced the evening prayer, as it is said: And he lighted upon the place (Gen. 28:11). The word vayifgah (“lighted upon”) alludes to prayer, as is said: Therefore, pray not thou … neither make intercession (tifga) (Jer. 7:16). And it is written concerning Daniel: And he kneeled upon his knees three times a day, and prayed (Dan. 6:11). However, in this verse, the time of prayer is not specified. It was David who came and set the time for prayer, by saying; Evening, and morning, and at noonday, will I complain and moan, and He hath heard my voice (Ps. 55:18). Therefore a man may not pray more than three times a day.