Genesis 1:5 (BSB)

God called the light “day,” and the darkness He called “night.” And there was evening, and there was morning—the first day.

From Genesis 1. Also in the ESV.

Commentary on Genesis 1:5

• John Calvin (Reformed), Calvin's Commentaries on Genesis 1:5: 5. And God called the light That is, God willed that there should be a regular vicissitude of days and nights; which also followed immediately when the first day was ended. For God removed the light from view, that night might be the commencement of another day.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Genesis 1:3-5: We have here a further account of the first day's work, in which observe, 1. That the first of all visible beings which God created was light; not that by it he himself might see to work (for the darkness and light are both alike to him), but that by it we might see his works and his glory in them, and might work our works while it is day.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Genesis 1:5: And God called the light day, and the darkness he called night,.... Either by the circulating motion of the above body of light, or by the rotation of the chaos on its own axis towards it, in the space of twenty four hours there was a vicissitude of light and darkness; just as there is now by the like motion either of the sun, or...
• Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Genesis 1:3-5: THE FIRST DAY. (Gen 1:3-5) God said--This phrase, which occurs so repeatedly in the account means: willed, decreed, appointed; and the determining will of God was followed in every instance by an immediate result. Whether the sun was created at the same time with, or long before, the earth, the dense accumulation of fogs and vapors which enveloped the chaos had covered the globe with a settled gloom.