The second example in doubtful matters: smoking.

The Shaykh : There are also things in this category that are doubtful regarding whether they fall under the ruling, such as smoking, for example. The smoking that is done now—cigarettes—is it forbidden or permissible? Yes.
I have one person who says it is disliked, another who says it is permissible, and another who says it is obligatory; we do not know. Yes, in any case, we look and we use analogy. Regarding smoking, some scholars said it is not forbidden, because Allah says: And is this something created in the earth or in the sky? It is in the earth, so it is a creation for us, and whatever is created for us is for us; we benefit from it as we wish, and no one prevents us from it. We say to them: then there are things that are created and are forbidden for you. What do you say about the pig? It is forbidden, and it is a creation. He said: The pig is forbidden because the text indicated its prohibition But where is the text that indicates the prohibition of this? It is permissible. The second person said: No, it is obligatory. How? He said: Because a person becomes dizzy if he does not smoke, and if he enters prayer while dizzy, he does not know what he is saying in his prayer; he must smoke so that he knows how to say it in his prayer. This is also a problem, and people differed on it. So is it among the doubtful matters, or not? Yes. If we go to the extreme and say it is among the doubtful matters, the Prophet (peace and blessings be upon him) said: What is it? But upon reflection, and after it became clear to people now that this smoke is harmful to health, thinking, behavior, and money, it became clear that it is forbidden and that it is not among the doubtful matters. It is true that there is no text in the Qur'an or the Sunnah that smoking is forbidden, because it did not occur except recently, but in the Qur'an and the Sunnah there are general principles that cover everything that occurs until the Day of Resurrection. It is harmful to health, and doctors have agreed that it is a cause of serious diseases, including cancer. Cancer is a fatal disease, and everyone shuns it as a sheep shuns the wolf. So this is the operative cause that subjects it to prohibition.
Second: It is harmful to the lungs, which is part of health. It is harmful to thinking, because if a person delays smoking, his mind becomes clouded and he has no thinking; perhaps he walks in the market and does not see people because he has been lost. This is also harm. It is harmful to money.