Is it permissible to buy tobacco for my father as he asks me to do so?
It is not permissible to buy anything prohibited for the sake of your father whether it is tobacco, opium, hashish, alcohol or the like even if he asks you to do so. It was authentically reported that the Prophet (peace be upon him) said:
There is no submission to a creature in matters involving disobedience to Allah.
He also said:
"Submission is obligatory only in what is good (and reasonable)."
But you have to advise and show him your excuse for not buying it in a polite way and with good manners. (Part No. 13; Page No. 65)
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.