Oral cancer is a highly lethal disease and one of the most debilitating and disfiguring of all malignancies in the world. According to Global Adult Tobacco Survey (GATS) 2010 report, 60% of tobacco users in India use only smokeless tobacco. Among 206 million smokeless tobacco users, 65.1 million are consuming gutkha. In recent years, gutkha is recognized as a life threatening disorder with the serious health consequences.
Below evidences have been taken from this thread and repeated here for the sake of understanding.
'Do not kill yourselves, Allah is indeed merciful to you.'
'Do not cast yourselves, with your own hands, into destruction.'
And the Messenger May Allah's peace and blessings be upon him says: 'No harm may be inflicted on oneself or others.'
(Ahmad and Ibn Maajah from Ibn Abbaas and Ubaadah)
'Whoever consumes poison, killing himself with it, then he will he consuming his poison in the hellfire, and he will abide in it permanently and eternally.'
(Al-Bukhari and Muslim from Jaabir)
Verily, the example of a good companion and a bad one is like that of a perfume merchant and a blacksmith: As for the perfume merchant, he would either grant you (some perfume), or you would buy (some perfume) from him, or (in the least) you would get a good smell from him. And as for the blower of the bellows (ironsmith), you would either get a foul odour from him, or he would burn your clothes.
(Al-Bukhari and Muslim)
'(The Prophet May Allah's peace and blessings be upon him) who will enjoin upon them the doing of what is right, forbid them the doing of what is wrong, make lawful to them the good things of life, prohibit for them the evil things, and lift from them their burdens and the shackles that were (previously) upon them.'
Allah's Messenger said: Indeed when Allah prohibits something, he prohibits eating its price.
(Ahmad and Abu Dawud)
“And it may be that you dislike a thing which is good for you and that you like a thing which is bad for you. Allah knows but you do not know.” (AI-Baqarah, 2:216)
A marfu' hadith from Abu Dawud and at-Tirmidhi, classified as sahih, where `A'isha (RA) stated, 'Every intoxicant is haraam and whatever damages the senses, causes addiction and numbs the senses.'
It is related by Imaam Ahmad, Abu Dawud from Umm Salamah (RA), who said, 'The Messenger forbid from every intoxicant and addictive thing that numbs the senses.' AlHaafiz az-Zain al`Iraaqi said, 'It's chain of narration is authentic and as-Suyuti classified it as Sahih in Jaami` us-Saghir.'
On a side note:
How smoking can be classed differently (Mufti Amjad Mohammed)