Which Day Is the Lord's Day?
By precept, the Lord's day, which is Ahayah's day, is on the 7th day of the week, which is known as the Sabbath.
Acts of John 6
But the Holy Spirit showed him to them as more cheerful. And on the seventh day, it being the Lord's day, he said to them: Now it is time for me also to partake of food.
Acts of peter 29
But Peter had appointed to be with Marcellus on the Lord's day, to see the widows even as Marcellus had promised, to minister unto them with his own hands. The lad therefore that was risen again said: I depart not from Peter. And his mother, glad and rejoicing, went unto her own house. And on the next day after the sabbath she came to Marcellus' house bringing unto Peter two thousand pieces of gold, and saying unto Peter: Divide these among the virgins of Christ which serve him.
By the evidence of the scriptures, the Lord's day was the Sabbath, the seventh day. Also, the records show that the Sabbath is Ahayah's holy day:
If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day; and call the sabbath a delight, the holy of Ahayah, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
(The Sabbath is his holy day, the holy of Ahayah, hence it is known as the Lord's day.)
 I was in the Spirit on the Lord's day, and heard behind me a great voice, as of a trumpet,
(The scriptures also confirm that the seventh day is the Sabbath, not the first day of the week.)
Six days ye shall gather it; but on the seventh day, which is the sabbath, in it there shall be
The Seventh day has been holy from the beginning and kept by Alahayim, his angels, and all the righteous who go out of the world: Apocalypse of Moses 44
And Michael came and taught Seth how to prepare Eve for burial. And there came three angels and they buried her body where Adam's body was and Abel's. And thereafter Michael spake to Seth and saith: "Lay out in this wise every man that dieth till the day of Resurrection." And after giving him this rule; he saith to him: "Mourn not beyond six days, but on the seventh day rest and rejoice on it, because on that very day Alahayim rejoiceth, yea, and we angels too with the righteous soul, who hath passed away from the earth."
By the grace of the Son of Alahayim, the Sabbath is also a day of rest for the unrighteous souls in punishments in hell:
Apocalypse of Paul 44
And after these things I saw the Son of Alahayim descending from heaven, and a diadem was on his head. And seeing him those who were placed in punishment exclaimed all with one voice saying: Have pity, Son of the High Alahayim! Thou art He who shewest refreshment for all in the heavens and on earth, and on us likewise have pity, for since we have seen Thee, we have refreshment. And a voice went out from the Son of Alahayim through all the punishments saying: And what work have ye done that ye demand refreshment from me? My blood was poured out for your sakes, and not even so did ye repent: for your sakes I wore the crown of thorns on my head: for you I received buffets on my cheeks, and not even so did ye repent. I asked water when hanging on the cross and they gave me vinegar mixed with gall, with a spear they opened my right side, for my name's sake they slew my prophets and just men, and in all these things I gave you a place of repentance and ye would not. Now, however, for the sake of Michael the archangel of my covenant and the angels who are with him, and because of Paul the well-beloved, whom I would not vex, for the sake of your brethren who are in the world and offer oblations, and for the sake of your sons, because my precepts are in them, and more for the sake of mine own kindness, on the day on which I rose from the dead, I give to you all who are in punishment a night and a day of refreshment forever. And they all cried out and said, We bless thee, Son of Alahayim, that Thou hast given us a night and a day of respite. For better to us is a refreshment of one day above all the time of our life which we were on earth, and if we had plainly known that this was intended for those who sin, we would have worked no other work, we would have done no business, and we would have done no iniquity: what need had we for pride in the world? For here our pride is crushed which ascended from our mouth against our neighbour: our plagues and excessive straitness and the tears and the worms which are under us, these are much worse to us than the pains which we have left behind us. When they said thus, the malign angels of the penalties were angered with them, saying: How long do ye lament and sigh? for ye had no pity. For this is the judgment of Alahayim who had no pity. But ye received this great grace of a day and a night's refreshment on the Lord's Day for the sake of Paul the well-beloved of Alahayim who descended to you.
For further edification, please visit the lessons:
Understanding the Sabbath:
Understanding the calendar: