3 Nephi 21

To those He visited in the Americas, the Savior said -

"...I give unto you a sign, that ye may know the time when these things shall be about to take place—that I shall gather in, from their long dispersion, my people, O house of Israel, and shall establish again among them my Zion...."  (Book of Mormon | 3 Nephi 21:1)

"...this is the thing which I will give unto you for a sign—for verily I say unto you that when these things which I declare unto you, and which I shall declare unto you hereafter of myself, and by the power of the Holy Ghost which shall be given unto you of the Father, shall be made known unto the Gentiles that they may know concerning this people who are a remnant of the house of Jacob, and concerning this my people who shall be scattered by them..."  (Book of Mormon | 3 Nephi 21:2)

The coming forth of the Book of Mormon is the sign...thus Israel is presently being gathered.

Also in fulfillment of this prophesy, in 1836, in the Kirtland Temple -

"...Moses appeared before us, and committed unto us the keys of the gathering of Israel from the four parts of the earth, and the leading of the ten tribes from the land of the north".  (Doctrine and Covenants | Section 110:11)