Paul did.
“I appeal to you, brothers, in the name of our Lord Jesus Christ, that all of you agree with one another so that there may be no divisions among you and that you may be perfectly united in mind and thought. My brothers, some from Chloe's household have informed me that there are quarrels among you. What I mean is this: One of you says, "I follow Paul"; another, "I follow Apollos"; another, "I follow Cephas"; still another, "I follow Christ."
Is Christ divided? Was Paul crucified for you? Were you baptized into the name of Paul? I am thankful that I did not baptize any of you except Crispus and Gaius, so no one can say that you were baptized into my name. (Yes, I also baptized the household of Stephanas; beyond that, I don't remember if I baptized anyone else.) For Christ did not send me to baptize, but to preach the gospel—not with words of human wisdom, lest the cross of Christ be emptied of its power. 1Cor 1:10-17
You could easily read the above as “One of you says, "I follow Luther"; another, "I follow Calvin"; another, "I follow Wesley"; still another, "I follow Christ."
Christians cannot be “perfectly united in mind and thought” when they have different beliefs on, say, the necessity of water baptism, while others believe “This is my Body” means “This is a cookie”
No he didn't. He was writing to the ekklesia at Corinth that they be all of one mind.