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 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. Also, the records show that the Sabbath is Ahayah's holy day, hence it is known as Ahayah's day or the Lord's 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
For further edification, please visit the lessons:
Understanding the Sabbath:
Understanding a full day: