And He placed on it [i.e., the earth] firmly set mountains over its surface, and He blessed it and determined therein its [creatures'] sustenance in four days without distinction1 - for [the information of] those who ask.
Translation: Saheeh International (English)
1 Also "four equal days" or "four days of completion."
He created firm mountains on it, which stabilise it and prevent it from shaking. And He proportioned the provisions of the people and animals by the fourth day, following on from the two previous days: Tuesday and Wednesday, equal for whoever wants to ask regarding it.