Is expiation obligatory for one who fondled his penis without intending masturbation, yet a drop was emitted, and he had sworn not to masturbate?

Masturbation is forbidden, and playing with the penis for the sake of lust is not permissible. Whoever does so must repent and offer an expiation for a broken oath (kaffarat yamin). Ghusl (ritual bath) is required upon the emission of semen, even if it is just a single drop.