What is the ruling on a father hitting his adult son, and what is the ruling on a father spitting on his son (whether adult or not)?

Scholars have differed on the permissibility of disciplining an adult child by striking them. Some have permitted it if the striking is effective in reforming them, citing the hadith of Aisha (may Allah be pleased with her) in which she mentioned that Abu Bakr struck her. Al-Hafiz said: "And in it is the disciplining of a man's daughter, even if she is married, grown, and outside his home." Al-Iraqi said: "In it is a man's disciplining of his child by word, deed, and striking, even if he is an adult or a grown, married woman." Others have deemed striking an adult impermissible, and this is understood from the كلام of the Shafi'is. The father should not spit on his child, as it contains humiliation that contradicts human dignity.