Negative commandment · Lo Ta’aseh #80 of 613
Not to ascend to the altar using steps
שלא לפסוע על המזבח
The verse · Shemot 20:23
וְלֹא־תַעֲלֶה בְמַעֲלֹת עַל־מִזְבְּחִי אֲשֶׁר לֹא־תִגָּלֶה עֶרְוָתְךָ עָלָיו
“Neither shalt thou go up by steps to my altar, that thy nakedness be not exposed on it.”
The Rambam’s words
Not to ascend to the altar using steps, as [Exodus 20:23] states: "Do not ascend My altar with steps."
שלא לפסוע על המזבח, שנאמר "וְלֹא תַעֲלֶה בְּמַעֲלוֹת עַל מִזְבְּחִי" (שמות כ, כב).
Who & when
“And [it] is practiced at the time of the [Temple] by males and females.”
Where in the Mishneh Torah
Hilchot The Chosen Temple הלכות בית הבחירה