the words which I had often heard my father speak concerning eternal life, and the of the saints, deep into my heart.Jacob spoke of eternal life (Jacob 6:11) as did many other Book of Mormon prophets. But as far as I could see, Jacob is the only Book of Mormon prophet speaking of the joy of the saints. 2 Nephi 9 contains his words.
2 Nephi 9:18
But, behold, the , the of the Holy One of Israel, they who have believed in the Holy One of Israel, they who have endured the of the world, and despised the shame of it, they shall the of God, which was prepared for them the foundation of the world, and their shall be full .2 Nephi 9:43
But the things of the wise and the shall be from them forever—yea, that happiness which is prepared for the saints.Of course, all Book of Mormon prophets said a lot of things that were never recorded on the plates. A fuller account might show others talking specifically about the joy of the saints. I still find it interesting, though, that Enos mentioned this particular topic that he had heard from his father and the only source for that in the Book of Mormon in fact is his father.