Footnotes to the 1981 LDS edition of the scriptures quote the following verses as an indication of the commandments that Lehi fulfilled:
For behold, they have rejected the words of the prophets. Wherefore, if my father should dwell in the land after he hath been commanded to flee out of the land, behold, he would also perish. Wherefore, it must needs be that he flee out of the land. (1 Ne. 3:18)
And we had obtained the records which the Lord had commanded us, and searched them and found that they were desirable; yea, even of great worth unto us, insomuch that we could preserve the commandments of the Lord unto our children. (1 Ne. 5:21)
And it came to pass that the Lord commanded him that I, Nephi, and my brethren, should again return unto the land of Jerusalem, and bring down Ishmael and his family into the wilderness. (1 Ne. 7:2)
While all three verses certainly represented fulfilled commandments, verse 8 seems more specifically to apply to the commandment to bring Ishmael’s family. Just after recording the marriages (v. 7), verse 8 begins with “and thus.” The marriages are the proof that the commandment has been fulfilled. While the original instruction does not specify that they should bring Ishmael’s family in order to marry the daughters, that implication must have been clear.