At the beginning of the Cause, for certain reasons, He smoked a little...

One of these last prohibitions is the smoking of tobacco, which is unclean, malodorous, disagreeable and vulgar and of which the gradual harmfulness is universally recognized. All clever physicians have judged, and have also shown by experiment, that one of the constituents of tobacco is a mortal poison and that smokers are exposed to different indispositions and maladies. That is why cleanly people have a marked aversion for its use.

His supreme Highness the Báb—may my soul be His sacrifice! —in the beginning of His Cause, openly forbade it and all the friends abandoned its use. But, as it was a time for caution and he who abstained from smoking was ill treated, persecuted and even killed, therefore the friends were obliged, as a matter of prudence, to smoke. Later, the Kitáb-i-Aqdas was revealed and as the prohibition of tobacco was not clearly stated in it, the friends did not renounce it. But the Blessed Perfection had always a marked aversion for its use. At the beginning of the Cause, for certain reasons, He smoked a little, but later He abandoned it completely, and the holy souls who obeyed Him in all circumstances, also entirely gave up smoking. I wish to say that, in the sight of God, the smoking of tobacco is a thing which is blamed and condemned, very unclean, and of which the result is by degrees injurious. Besides it is a cause of expense and of loss of time and it is a harmful habit. So, for those who are firm in the Covenant, it is a thing reprobated by the reason and by tradition, the renouncement of which giveth gradual repose and tranquility, permitteth one to have stainless hands and a clean mouth, and hair which is not pervaded by a bad odor.


- Abdul Baha

http://reference.bahai.org/en/t/c/BWF/bwf-36.html