Does smoking invalidate the ablution, and what is the ruling on chewing qat?

This is a letter we received from Abu Bakr Saleh Dawud Hussein, a Sudanese resident in the Hufar al-Batin region of the Kingdom. He says: If a person performs ablution, then smokes and prays immediately, and perhaps leads people in prayer, and we have told those who do this that smoking invalidates the ablution, but they said to us: That is not correct. What is the ruling in this matter?
Answer: Smoking does not invalidate the ablution, but it is forbidden and foul, and it must be abandoned. However, if he smokes and prays, his prayer is not invalidated and his ablution is not invalidated; because it is a type of the known hashish, but it is forbidden due to its harm.
It is obligatory for one who uses it to guard against it, leave it, and fear its evil. It is not permissible for him to buy it or use it, nor is trade in it permissible. Rather, it is obligatory for one who engages in that to repent to Allah and leave trade in it. Allah the Exalted said: [Al-Ma'idah: 4]. Allah (Mighty and Majestic) said: [Al-Ma'idah: 4]. So Allah (Mighty and Majestic) has not made lawful for us except the good things, which are the nourishing and beneficial ones.
And He the Exalted said in describing the Prophet (peace and blessings be upon him): [Al-A'raf: 157].
And there is no doubt that smoking and all intoxicants are from the foul things, and likewise the known intoxicating hashish is from the foul things, so it must be abandoned.
And likewise the qat known in Yemen is from the foul things; because it causes great harm and leads to the wasting of times and the loss of times. A group of those with knowledge of it, from the sons of Yemen and others, have mentioned many harms in it. So it is obligatory for the one who uses it to leave it, and to repent to Allah from it, and to preserve his health, his wealth, and his times in what benefits him. It is obligatory for the believer not to waste his times in vain, and this qat wastes times and harms its user, and destroys his wealth in vain.
So it is obligatory for the believer to beware of what harms him in his religion and his worldly life, and among that is smoking and qat, and types of intoxicants; it is necessary to beware of all of them with sincere and earnest repentance from what has passed. Trade in that is not permissible, rather it is obligatory to leave it and not trade in it; because it harms the Muslims. We ask Allah for guidance and success for everyone.
The presenter: May Allah reward you.