Does bringing cigarettes to a smoking father cause the son to fall into sin, and if so, how can the son refuse the father’s request and advise him?

It is not permissible to bring or buy cigarettes for one's father, or to hand them to him, because smoking is forbidden (haram), and assisting in consuming it is also forbidden. Whoever does so is sinful. Sheikh al-Islam Ibn Taymiyyah stated that whoever assists in disobeying Allah is sinful, citing the Prophet's (peace be upon him) cursing of alcohol and those who assist in its consumption. Similarly, Sheikh Ibn 'Uthaymeen issued a fatwa that one should not obey a father if he orders the purchase of cigarettes, because there is no obedience to a created being in disobeying the Creator, unless the father promises gradual repentance from smoking. It is appropriate to advise the father who commits a forbidden act and to explain the impermissibility of committing such a sin.