1 Samuel 20:5

So David told him, “Look, tomorrow is the New Moon, and I am supposed to dine with the king. Instead, let me go and hide in the field until the third evening from now.

Note That is, the New Moon feast; also in verses 18, 24, and 27

BSB · Berean Standard Bible
And David said unto Jonathan, Behold, to morrow is the new moon, and I should not fail to sit with the king at meat: but let me go, that I may hide myself in the field unto the third day at even.
KJV · King James Version
David said to Jonathan, “Behold, tomorrow is the new moon, and I should not fail to dine with the king; but let me go, that I may hide myself in the field to the third day at evening.
WEB · World English Bible
And David said unto Jonathan, Behold, to-morrow is the new moon, and I should not fail to sit with the king at meat: but let me go, that I may hide myself in the field unto the third day at even.
ASV · American Standard Version

Related passages

From the Treasury of Scripture Knowledge, grouped by the word they explain.

the new moon
The months of the Hebrews were lunar months, and they reckoned from one new moon to another: and, as their feasts, particularly the passover, were reckoned according to this, they were very scrupulous in observing the first appearance of each new moon. On these new moons, they offered sacrifices, and feasted together: but the gathering together of all the families of a tribe on such occasions seems to have taken place only once in the year.
1 Samuel 20:6; Numbers 10:10; Numbers 28:11; 2 Kings 4:23; Psalm 81:3; Colossians 2:16
that I may
1 Samuel 20:19; 1 Samuel 19:2; Psalm 55:12; Proverbs 22:3; John 8:59; Acts 17:14