I lay prostrate before the LORD those forty days and forty nights because the LORD had said he would destroy you.--Deuteronomy 9:25 (NIV)
When Moses heard God's decree of judgment on the Israelites for their sin of worshipping the golden calf, he prayed passionately for their salvation. Moses was clear of guilt in this sin, but he prayed that God would "overlook the stubbornness of this people, their wickedness and their sin" (v. 27). And he didn't just pray a quick prayer every morning. He prayed desperately--on his face before the Lord, eating no food and drinking no water (v.18), for forty days and forty nights! The fact that he mentioned days and nights makes me think that Moses was probably praying around the clock for almost a month and a half.
Moses didn't get discouraged after five weeks of constant prayer and fasting had seen no answer. He persevered in his prayer until God answered him. May we do the same.