3 Nephi 26

 Mormon tells that -

"...now there cannot be written in this book even a hundredth part of the things which Jesus did truly teach unto the people;

7 But behold the plates of Nephi do contain the more part of the things which he taught the people.

8 And these things have I written, which are a lesser part of the things which he taught the people; and I have written them to the intent that they may be brought again unto this people, from the Gentiles, according to the words which Jesus hath spoken."  (3 Nephi 26:6–8)

Adding - 

"Behold, I was about to write them, all which were engraven upon the plates of Nephi, but the Lord forbade it, saying: I will try the faith of my people."  (3 Nephi 26:11)

Obviously, there are many more teachings that Christ gave that we presently may not have.