[i] If a person commits, due to ignorance, an act which invalidates the fast, and if it was within his means and ability to learn the issue (culpable ignorance), he should, as an obligatory precaution, give the Kaffara. And if he could learn the issue or he could not notice it or he was sure that a certain thing/ act does not invalidate the fast (inculpable ignorance), it is not obligatory on him to give Kaffara. (Tawazih al-Masail (with annotations by Imam Khomeini), vol.1, p. 927, issue No. 1659. For further information in this regard, refer to question 2668 (site: 3319).

[ii] Tawazih al-Masail (with annotations by Imam Khomeini), vol.1, p. 935, issue No. 1678. If a man who is fasting in the month of Ramadhan has sexual intercourse with his wife who is also fasting and if he has compelled her for that, he should give Kaffarah for his own fast and as a precaution, also for his wife's. And if she had wilfully consented to the sexual intercourse, a Kaffarah becomes obligatory on each of them.

[iii]  Tawazih al-Masail (with annotations by Imam Khomeini), vol.1, p.891, issue No. 1572.