Luke 4:1-4 (KJV)
1 And Jesus being full of the Holy Ghost returned from Jordan, and was led by the Spirit into the wilderness,
2 Being forty days tempted of the devil. And in those days he did eat nothing: and when they were ended, he afterward hungered.
3 And the devil said unto him, If thou be the Son of God, command this stone that it be made bread.
4 And Jesus answered him, saying, It is written, That man shall not live by bread alone, but by every word of God.
Matthew 6:16-18 (KJV)
16 Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward.
17 But thou, when thou fastest, anoint thine head, and wash thy face;
18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.
Matthew 9:14-15 (NKJV)
14 Then the disciples of John came to Him, saying, “Why do we and the Pharisees fast often, but Your disciples do not fast?”
15 And Jesus said to them, “Can the friends of the bridegroom mourn as long as the bridegroom is with them? But the days will come when the bridegroom will be taken away from them, and then they will fast.
Luke 18:9-14 (NIV)
9 To some who were confident of their own righteousness and looked down on everyone else, Jesus told this parable:
10 “Two men went up to the temple to pray, one a Pharisee and the other a tax collector.
11 The Pharisee stood by himself and prayed: ‘God, I thank you that I am not like other people—robbers, evildoers, adulterers—or even like this tax collector.
12 I fast twice a week and give a tenth of all I get.’
13 “But the tax collector stood at a distance. He would not even look up to heaven, but beat his breast and said, ‘God, have mercy on me, a sinner.’
14 “I tell you that this man, rather than the other, went home justified before God. For all those who exalt themselves will be humbled, and those who humble themselves will be exalted.”
Joel 2:12-13 (NIV)
12 “Even now,” declares the Lord, “return to me with all your heart, with fasting and weeping and mourning.”
13 Rend your heart and not your garments. Return to the Lord your God, for he is gracious and compassionate, slow to anger and abounding in love, and he relents from sending calamity.