Alma 5

 Alma told the saints in Zarahemla - 

"Behold, I say unto you they are made known unto me by the Holy Spirit of God. Behold, I have fasted and prayed many days that I might know these things of myself. And now I do know of myself that they are true; for the Lord God hath made them manifest unto me by his Holy Spirit; and this is the spirit of revelation which is in me.

47 And moreover, I say unto you that it has thus been revealed unto me, that the words which have been spoken by our fathers are true, even so according to the spirit of prophecy which is in me, which is also by the manifestation of the Spirit of God."  (Alma 5:46–47)

Alma expresses that he knows the truth taught by the fathers is true by the "spirit of prophecy" manifested by the Holy Ghost.  It reminds me of the testimony of the angel to John that he  - 

"...and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy."  (Revelation 19:10)

I believe that holds true in my calling that a testimony of Jesus is the spirit of prophecy.