Is smoking considered a major sin?

Smoking is unlawful (haram (definition)), and one should not be lenient with a sin on the pretext that it is not among the major sins. For minor sins, when accumulated, can be destructive, and persistence in a minor sin transforms it into a major one. As some of the righteous predecessors said: "Do not look at the smallness of the sin, but look at the greatness of the One Whom you have disobeyed." The Prophet, peace and blessings be upon him, warned against belittling sins. Therefore, a smoker should hasten to repent and strive against their self to quit smoking.