Contradiction with James 4:9
James speaks of afflicting oneself, mourning, and showing sorrow openly, which contrasts with the instruction in Matthew 6:17 to maintain a cheerful appearance while fasting.
James 4:9: Be afflicted, and mourn, and weep: let your laughter be turned to mourning, and [your] joy to heaviness.
Contradiction with Joel 2:12-13
The call to rend hearts, show mourning, and return to God with external displays contrasts with Matthew 6:17's directive to anoint and wash, avoiding outward signs of fasting.
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: