New Living Translation
John had been telling Herod, “It is against God’s law for you to marry your brother’s wife.”

American Standard Version
For John said unto Herod, It is not lawful for thee to have thy brother's wife.

Berean Study Bible
For John had been telling Herod, “It is not lawful for you to have your brother’s wife!”

Douay-Rheims Bible
For John said to Herod: It is not lawful for thee to have thy brother's wife.

English Revised Version
For John said unto Herod, It is not lawful for thee to have thy brother's wife.

King James Bible
For John had said unto Herod, It is not lawful for thee to have thy brother's wife.

World English Bible
For John said to Herod, "It is not lawful for you to have your brother's wife."

Young's Literal Translation
for John said to Herod -- 'It is not lawful to thee to have the wife of thy brother;'

Mark 6:18 Additional Translations ...