This is a totally untrue statement.
Cardinal Hosius (Catholic, 1524), President of the Council of Trent:
"Were it not that the baptists have been grievously tormented and cut off with the knife
during the past twelve hundred years, they would swarm in greater number than all the Reformers.
" (Hosius, Letters, Apud Opera, pp. 112, 113.)
The "twelve hundred years" were the years preceding the Reformation in which Rome persecuted Baptists with the most cruel persecution thinkable.
Sir Isaac Newton:
"The Baptists are the only body of known Christians that have never symbolized with Rome."
Mosheim (Lutheran):
"Before the rise of Luther and Calvin, there lay secreted in almost all the countries of Europe persons who adhered tenaciously to the principles of modern Dutch Baptists."
Edinburg Cyclopedia (Presbyterian):
"It must have already occurred to our readers that the Baptists are the same sect of Christians that were formerly described as Ana-Baptists.
Indeed this seems to have been their leading principle from the time of Tertullian to the present time."
Tertullian was born just fifty years after the death of the Apostle John.
Your source?