大般涅槃經疏 18.21

18.21

「云何念天」下，即第六念。或謂當果第一義天。今謂不爾。通念諸天，直是念天不云當果。當果天與前佛果無異，正是通念。此世天境，隨義別立，故名為天。

From "What is mindfulness of the gods?" onwards is the sixth recollection. Some take it to mean the heaven of the paramārthasatya as the future fruit. We now say this is not so. It is a general mindfulness of all the devas, simply being mindfulness of the gods without speaking of the future fruit. The heaven of the future fruit is no different from the prior buddha fruit; it is precisely a general mindfulness. As for the heavenly realms of this world, they are established distinctly according to their specific meanings, and are thus termed "devas."