Midrash sa Mga Awit 106:12: Midrash Tanchuma & Shemot Rabbah

In the future exiles will not be redeemed except as a reward for faithfulness, as it is said: Come with me from Lebanon, my bride, with me from Lebanon; look from the top of Amana (Song 4:8). It says likewise: And I will betroth thee unto Me in faithfulness (Hos. 2:28). Thus you learn that faith is powerful, for in reward for faith, the Shekhinah hovered over them and they sang the song, as it is said: And they believed in the Lord … and Moses sang (Exod. 14:31–15:1), and it says also: Then believed they his words; they sang his praise (Ps. 106:12).

What did Aaron do then? He said: Let the celebration be delayed until tomorrow, as it is said: And Aaron made proclamation and said: “Tomorrow shall be a feast to the Lord” (Exod. 32:5). Whereupon the Holy Spirit called out: Hasten, descend, they have forgotten what I did for them. The Holy One, blessed be He, said: In this world they have sinned because of the evil inclination within them, but in the time-to-come I will remove it from them, as is said: And I will take away the strong heart of your flesh (Exod. 36:26).

Another matter, “then Moses…sang” – that is what is written: “They believed in His words, they sang His praise” (Psalms 106:12). Rabbi Abahu said: Although it is written that they already believed while they were in Egypt, as it is stated: “The people believed” (Exodus 4:31), they subsequently did not believe, as it is stated: “Our ancestors in Egypt did not comprehend Your wonders” (Psalms 106:7). When they came to the sea and saw the might of the Holy One blessed be He, how He administers justice to the wicked, as you say: “My hand grasps judgment” (Deuteronomy 32:41), and He sunk the Egyptians in the sea, immediately: “They believed in God” (Exodus 14:31). Due to that belief, the Divine Spirit rested upon them and they sang a song. That is what is written: “Then [az] Moses and the children of Israel sang.” Az means nothing other than faith, as it is stated: “It was from when [me’az] he appointed him in his house” (Genesis 39:5), and it is written: “Everything he had he placed in his hands” (Genesis 39:4).²When Potiphar trusted Joseph fully and placed him in charge of his entire household, the verse uses the word az in stating that Potiphar appointed Joseph in his house. That is: “They believed in His words, they sang His praise.”