Contradiction with Matthew 5:14-16
This passage encourages letting your light shine before men, potentially contradicting the private nature of fasting described in Matthew 6:16.
Matthew 5:14-16: Ye are the light of the world. A city that is set on an hill cannot be hid.
Contradiction with Luke 18:9-14
The publican's humble approach in contrast to the Pharisee's boastfulness parallels fasting in humility rather than in the show, potentially contradicting the notion of hiding one's spiritual disciplines.
Luke 18:9-14: And he spake this parable unto certain which trusted in themselves that they were righteous, and despised others: [that...: or, as being righteous]
Contradiction with 1 Samuel 16:7
God looks at the heart rather than outward appearances, suggesting a potential contradiction to the emphasis on external appearances in Matthew 6:16.
1 Samuel 16:7: But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for [the LORD seeth] not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart. [outward...: Heb. eyes]
Contradiction with Isaiah 58:5
Critiques fasting for show, which correlates with and potentially contradicts the warning against being as hypocrites in Matthew 6:16 in a broader spiritual context.
Isaiah 58:5: Is it such a fast that I have chosen? a day for a man to afflict his soul? [is it] to bow down his head as a bulrush, and to spread sackcloth and ashes [under him]? wilt thou call this a fast, and an acceptable day to the LORD? [a day...: or, to afflict his soul for a day?]
Contradiction with Joel 2:12-13
Calls for sincere repentance and heart change, which could be seen as differing from the caution against outward displays found in Matthew 6:16.
Joel 2:12-13: Therefore also now, saith the LORD, turn ye [even] to me with all your heart, and with fasting, and with weeping, and with mourning: