Daniel 10:2-3 says, "In those days I Daniel was mourning three full weeks. I ate no pleasant bread, neither came flesh nor wine in my mouth, neither did I anoint myself at all, till three whole weeks were fulfilled."
Arthur Wallis said, "Fasting is calculated to bring a note of urgency and importunity into our praying, and to give force to our pleading in the court of heaven. The man who prays with fasting is giving heaven notice that he is truly in earnest… Not only so, but he is expressing his earnestness in a divinely-appointed way. He is using a means that God has chosen to make his voice to be heard on high."