The System of the Vedanta according to Badarayana's Brahma-Sutras and Cankara's Commentary c10.s5.t2.2

c10.s5.t2.2

For this artery and the Sun are according to Chând. 8, 6, 2. (above p. 162), constantly connected by a ray (raçmi), “as “two villages are by a road” and by this the knower ascends (p. 1105, 12). Whether it is day or night when he dies, is all the same, since this connection of the artery with the ray persists as long as the body (p. 1106, 7). And that this ray is present even at night, can be perceived by the fact that in summer it is warm at night also; at other seasons it is less noticeable because the rays are too weak (p. 1106, 12). Were the ray not present at night one would have to assume either that the knower can ascend even without a ray,—in that case the ray would be altogether superfluous,—or that some of the knowers, those, namely, who die at night time, do not ascend at all, whereby the fruit of knowledge would become conditional (pâkshika); which cannot be admitted (p. 1107, 1. 4). And further it cannot be assumed that he who dies at night awaits the return of day, because by then, as the body is burnt in the meanwhile, there may no longer be any body capable of connection with the ray (p. 1107, 6; whence it seems to follow that the burning of bodies followed quickly upon the occurrence of death; cf. the note above p. 352).