The Doctrine and Covenants, Section 103:15-21

15 Behold, I say unto you, the redemption of Zion must needs come by power;

16 Therefore, I will raise up unto my people a man, who shall lead them like as Moses led the children of Israel.

17 For ye are the children of Israel, and of the seed of Abraham, and ye must needs be led out of bondage by power, and with a stretched-out arm.

18 And as your fathers were led at the first, even so shall the redemption of Zion be.

19 Therefore, let not your hearts faint, for I say not unto you as I said unto your fathers: Mine angel shall go up before you, but not my presence.

20 But I say unto you: Mine angels shall go up before you, and also my presence, and in time ye shall possess the goodly land.

21 Verily, verily I say unto you, that my servant Joseph Smith, Jun., is the man to whom I likened the servant to whom the Lord of the vineyard spake in the parable which I have given unto you.

Doctrine and Covenants Student Manual, Section 103

There have been many conjectures concerning [the leader referred to in verse 16]. There have even been misguided men who have declared themselves to be this man ‘like as Moses.’ Yet, the meaning as set forth in the scriptures, is very simple. In modern revelation the President of the Church is frequently compared to Moses. Soon after the organization of the Church, the Lord said, ‘no one shall be appointed to receive commandments and revelations in this church excepting my servant Joseph Smith, Jun., for he receiveth them even as Moses’ (D&C 28:2) In one of the great revelations upon Priesthood, this is more specifically expressed: ‘the duty of the President of the office of the High Priesthood is to preside over the whole church, and to be like unto Moses’ (D&C 107:91). … The man like unto Moses in the Church is the President of the Church. — Quote by John A. Widtsoe

Journal of Discourses, Orson Pratt 15:45

Whether that man is now in existence, or whether it is someone yet to be born; or whether it is our present leader who has led us forth into these valleys of the mountains, whether God will grant unto us the great blessing to have his life spared to lead forth his people like a Moses, we perhaps may not all know. … But be this as it may, whether he [Joseph Smith] is the man, whether President Young is the man, or whether the Lord shall hereafter raise up a man, for that purpose, we do know that when that day comes the Lord will not only send his angels before the army of Israel, but his presence will also be there.

Journal of Discourses, Orson Pratt 21:18

Indeed, before we can go back to inherit this land [in Jackson County, Missouri] in all its fulness of perfection, God has promised that he would raise up a man like unto Moses. Who this man will be I do not know; it may be a person with whom we are entirely unacquainted; it may be one of our infant children; it may be some person not yet born; it may be someone of middle age. But suffice it to say, that God will raise up such a man, and he will show forth his power through him, and through the people that he will lead forth to inherit that country, as he did through our fathers in the wilderness.