Is this explained in the Pali Canon?
Then the Blessed One went with a large number of monks to the Black Rock on the slope of Isigili. From afar he saw Ven. Vakkali lying dead on a couch. Now at that time a smokiness, a darkness was moving to the east, moving to the west, moving to the north, the south, above, below, moving to the intermediate directions. The Blessed One said, “Monks, do you see that smokiness, that darkness …?” “Yes, Lord.” “That is Mara, the Evil One. He is searching for the consciousness of Vakkali the clansman: “Where is the consciousness of Vakkali the clansman established?” But, monks, it is through unestablished consciousness that Vakkali the clansman has become totally unbound.”— SN 22:87