There are numerous passages that either explicitly or implicitly state that Christians are to hold to correct doctrine.
1Ti 4:1 Now the Spirit expressly says that in latter times some will depart from the faith, giving heed to deceiving spirits and doctrines of demons,
1Ti 4:2 speaking lies in hypocrisy, having their own conscience seared with a hot iron,
1Ti 4:3 forbidding to marry, and commanding to abstain from foods which God created to be received with thanksgiving by those who believe and know the truth. (NKJV)
2Ti 3:16 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, (NKJV)
Jud 1:3 Beloved, while I was very diligent to write to you concerning our common salvation, I found it necessary to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints. (NKJV)
Actually, it could be said that all Scripture implies that Christians are to hold to specific doctrine, hence it's writing, inspiration and canonization. Of course we cannot be so rigid as to think that that is all there is to it, lest it become a mere list of rules producing a dead faith. There is more to it than mere intellectual assent but neither can we deny that there are certain things Christians must believe.