The majority view (as far as I know) on smoking tobacco is that it is haraam.
But what is the rationale or evidence/proof behind that ruling?
There is no explicit ayah or hadith about smoking.
The goals of Islam (maqaasid ash-shari'ah, if I'm not mistaken) are five. Among those five are preservation of human life.
The history is interesting: the default ruling on all non-worship things is that they are mubah (permissible) until proven guilty. As with smoking.
When scholars initially investigated smoking, they found that: it causes bad breath, bad smells, blackened teeth. There are hadith about cleanliness, and specifically bad smells; so barring further evidence, they decided it's makrooh (no reward/sin to do it, but reward to avoid it).
Then along came medical science, which conclusively proved the link between smoking and lung damage, smoking and unhealth, smoking and cancer. Given the goal of preserving life, it became clear that smoking is haram because it harms you, severely.
O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent. And do not kill yourselves [or one another]. Indeed, Allah is to you ever Merciful. (Surah Nisaa, verse 29)
For more details, see this excellent reference question on Islam-QA.
There is no ayats or hadiths directly related to smoking. But, there are ayats and hadiths related to wasting your life and energy for small Earthly desires.
وَمَا كَانَ لِنَفْسٍ أَنْ تَمُوتَ إِلاَّ بِإِذْنِ الله كِتَابًا مُّؤَجَّلاً وَمَن يُرِدْ ثَوَابَ الدُّنْيَا نُؤْتِهِ مِنْهَا وَمَن يُرِدْ ثَوَابَ الآخِرَةِ نُؤْتِهِ مِنْهَا وَسَنَجْزِي الشَّاكِرِينَ
And it is not [possible] for one to die except by permission of Allah at a decree determined. And whoever desires the reward of this world - We will give him thereof; and whoever desires the reward of the Hereafter - We will give him thereof. And we will reward the grateful.
Ali Imran 145 (3/145)
مَن كَانَ يُرِيدُ حَرْثَ الْآخِرَةِ نَزِدْ لَهُ فِي حَرْثِهِ وَمَن كَانَ يُرِيدُ حَرْثَ الدُّنْيَا نُؤتِهِ مِنْهَا وَمَا لَهُ فِي الْآخِرَةِ مِن نَّصِيبٍ
Whoever desires the harvest of the Hereafter - We increase for him in his harvest. And whoever desires the harvest of this world - We give him thereof, but there is not for him in the Hereafter any share.
Shura 20 (42/20)
مَّن كَانَ يُرِيدُ ثَوَابَ الدُّنْيَا فَعِندَ اللّهِ ثَوَابُ الدُّنْيَا وَالآخِرَةِ وَكَانَ اللّهُ سَمِيعًا بَصِيرًا
Whoever desires the reward of this world - then with Allah is the reward of this world and the Hereafter. And ever is Allah Hearing and Seeing.
Nisa 134 (4/134)
مَّن كَانَ يُرِيدُ الْعَاجِلَةَ عَجَّلْنَا لَهُ فِيهَا مَا نَشَاء لِمَن نُّرِيدُ ثُمَّ جَعَلْنَا لَهُ جَهَنَّمَ يَصْلاهَا مَذْمُومًا مَّدْحُورًا
Whoever should desire the immediate - We hasten for him from it what We will to whom We intend. Then We have made for him Hell, which he will [enter to] burn, censured and banished.
Isra 18 (17/18)
A Mumin doesn't, a Muslim mustn't change his capital wealth (his energy, health, money, etc) for small and temporary delights of this dunya. Smoking is nothing but wasting one's capital wealth for sure. I cannot directly call it haram, but it looks to be so.
i use my answer from other question.
In addition to being harmful, as said in other answer, there are other reasons: