The Gemara attributes the institution of the three daily prayers to the Avos — Avraham instituted Shacharit, Yitzchak Mincha, and Yaakov Maariv — indicating the Avos practiced mitzvot on their own initiative.
אִיתְּמַר, רַבִּי יוֹסֵי בְּרַבִּי חֲנִינָא אָמַר: תְּפִלּוֹת אָבוֹת תִּקְּנוּם. רַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי אָמַר: תְּפִלּוֹת כְּנֶגֶד תְּמִידִין תִּקְּנוּם. תַּנְיָא כְּווֹתֵיהּ דְּרַבִּי יוֹסֵי בְּרַבִּי חֲנִינָא, וְתַנְיָא כְּווֹתֵיהּ דְּרַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי. תַּנְיָא כְּווֹתֵיהּ דְּרַבִּי יוֹסֵי בְּרַבִּי חֲנִינָא: אַבְרָהָם תִּקֵּן תְּפִלַּת שַׁחֲרִית, שֶׁנֶּאֱמַר: ״וַיַּשְׁכֵּם אַבְרָהָם בַּבֹּקֶר אֶל הַמָּקוֹם אֲשֶׁר עָמַד שָׁם״, וְאֵין ״עֲמִידָה״ אֶלָּא תְּפִלָּה, שֶׁנֶּאֱמַר: ״וַיַּעֲמֹד פִּינְחָס וַיְפַלֵּל״. יִצְחָק תִּקֵּן תְּפִלַּת מִנְחָה, שֶׁנֶּאֱמַר ״וַיֵּצֵא יִצְחָק לָשׂוּחַ בַּשָּׂדֶה לִפְנוֹת עָרֶב״, וְאֵין ״שִׂיחָה״ אֶלָּא תְּפִלָּה, שֶׁנֶּאֱמַר ״תְּפִלָּה לְעָנִי כִי יַעֲטֹף וְלִפְנֵי ה׳ יִשְׁפֹּךְ שִׂיחוֹ״. יַעֲקֹב תִּקֵּן תְּפִלַּת עַרְבִית, שֶׁנֶּאֱמַר: ״וַיִּפְגַּע בַּמָּקוֹם וַיָּלֶן שָׁם״, וְאֵין ״פְּגִיעָה״ אֶלָּא תְּפִלָּה, שֶׁנֶּאֱמַר: ״וְאַתָּה אַל תִּתְפַּלֵּל בְּעַד הָעָם הַזֶּה וְאַל תִּשָּׂא בַעֲדָם רִנָּה וּתְפִלָּה וְאַל תִּפְגַּע בִּי״
The dispute between the Rabbis and Rabbi Yehuda with regard to the times beyond which the different prayers may not be recited is rooted in a profound disagreement, also manifest in a later amoraic dispute. It was stated: Rabbi Yosei, son of Rabbi Ḥanina, said: The practice of praying three times daily is ancient, albeit not in its present form; prayers were instituted by the Patriarchs. However, Rabbi Yehoshua ben Levi said that the prayers were instituted based on the daily offerings sacrificed in the Holy Temple, and the prayers parallel the offerings, in terms of both time and characteristics. The Gemara comments: It was taught in a baraita in accordance with the opinion of Rabbi Yosei, son of Rabbi Ḥanina, and it was taught in a baraita in accordance with the opinion of Rabbi Yehoshua ben Levi. The Gemara elaborates: It was taught in a baraita in accordance with the opinion of Rabbi Yosei, son of Rabbi Ḥanina: Abraham instituted the morning prayer, as it is stated when Abraham came to look out over Sodom the day after he had prayed on its behalf: “And Abraham rose early in the morning to the place where he had stood before the Lord” (Genesis 19:27), and from the context as well as the language utilized in the verse, the verb standing means nothing other than prayer, as this language is used to describe Pinehas’ prayer after the plague, as it is stated: “And Pinehas stood up and prayed and the plague ended” (Psalms 106:30). Clearly, Abraham was accustomed to stand in prayer in the morning. Isaac instituted the afternoon prayer, as it is stated: “And Isaac went out to converse [lasuaḥ] in the field toward evening” (Genesis 24:63), and conversation means nothing other than prayer, as it is stated: “A prayer of the afflicted when he is faint and pours out his complaint [siḥo] before the Lord” (Psalms 102:1). Obviously, Isaac was the first to pray as evening approached, at the time of the afternoon prayer. Jacob instituted the evening prayer, as it is stated: “And he encountered [vayifga] the place and he slept there for the sun had set” (Genesis 28:11). The word encounter means nothing other than prayer, as it is stated when God spoke to Jeremiah: “And you, do not pray on behalf of this nation and do not raise on their behalf song and prayer, and do not encounter [tifga] Me for I do not hear you” (Jeremiah 7:16). Jacob prayed during the evening, after the sun had set.