Midrash sur Les Proverbes 8:17

Law: A Jewish person who does not pray the morning prayer, or the Musaf prayer, or the afternoon prayer, many times; that he didn't have time for prayer, or he abridged it to take care of his [toilet] needs, or he had traveled and forgot to pray: Which time is permitted for him to pray and fulfill his obligation? What is he required to do? So taught the sages: The morning prayer is til midday, the afternoon prayer til nightfall, evening prayer has no fixed [time]. But for the Musaf [prayers], all day. Rabbi Elazar said: [If] he forgot and did not pray the Musaf prayer, and he came to pray the afternoon prayer, he should pray the afternoon prayer and afterward the Musaf prayer. Why? For everything was created for its time. The evening prayer has no fixed [time], until dawn. Why? As it is written, (Proverbs 8:17), "I love those who love me and those who seek me find me." And all those who pray and set their hearts [in concentration] for prayer, it is a good sign that his prayer is accepted, as it says, (Psalms 10:17) "You hear the desire of the afflicted..." Great is prayer before the Holy One, blessed be He. Rabbi Elazar said, "Do you want to know the power of prayer? If it does not accomplish the whole [request], it accomplishes half of it. [To illustrate, when] Cain overtook his brother Abel and murdered him, a [divine] decree went out, (Genesis 4:12) 'You will be a restless wanderer (na v'nad) on earth.' Immediately, he stood and confessed before the Holy One, blessed be He, as it says, (Genesis 4:13) 'My punishment is more than one can bear.' He said before Him: Master of the World! You bear the whole world, yet my sin You cannot bear? You wrote, (Micah 7:18) 'Who bears sin and forgives the transgression,' forgiving the great sinner. Immediately, he found kindness before the Holy One, blessed be He, and He held back the "restlessness" (na), half the decree, and so it is written (Genesis 4:16) 'And he dwelled in the land of Nod [wandering, but not na, restlessness]. From here you learn that prayer is held great before the Holy One, blessed be He. And so for Hezekiah, when He told him, (II Kings 20:1) 'Put your house in order, because you are going to die...' immediately (II Kings 20:2) 'Hezekiah turned his face to the wall [and prayed to God]...' The Holy One, blessed be He, said to him: (II Kings 20:5-6) 'I have heard your prayer... I have added 15 years for your life...' So is it written, (Psalms 145:19) 'He fulfills the desires of those who fear him; he hears their cry and saves them.'"