Contradiction with Matthew 6:1
John 4:28 shows a public act of testimony, while Matthew 6:1 advises against public displays of piety.
Matthew 6:1: Take heed that ye do not your alms before men, to be seen of them: otherwise ye have no reward of your Father which is in heaven. [alms: or, righteousness] [of your: or, with your]
Contradiction with Proverbs 21:23
John 4:28 implies speaking openly about a personal experience, whereas Proverbs 21:23 promotes guarding one's words.
Proverbs 21:23: Whoso keepeth his mouth and his tongue keepeth his soul from troubles.
Contradiction with James 1:19
John 4:28 involves quick action and speech, while James 1:19 encourages being quick to listen and slow to speak.
James 1:19: Wherefore, my beloved brethren, let every man be swift to hear, slow to speak, slow to wrath:
Contradiction with Luke 5:14
John 4:28 highlights sharing an experience with others, whereas Luke 5:14 instructs to keep certain deeds confidential.
Luke 5:14: And he charged him to tell no man: but go, and shew thyself to the priest, and offer for thy cleansing, according as Moses commanded, for a testimony unto them.