My father is married to a second woman. My mother is angry at this. The second woman came and lived with my father and I. Is it Haram to lie on my mother about this to avoid conflicts?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, is His slave and Messenger.

Lying is prohibited; rather, it is a grave, major sin. Therefore, it is impermissible to lie, especially to one’s mother; the prohibition of lying is further emphasized in this case. If you can avoid lying by resorting to Tawriyyah. [For more benefit on the definition of Tawriyyah, please refer to Fataawa 367429 and 351313], then you should do so.

You should not resort to outright lying unless it is the only way to achieve your objective and provided that it does not incur any harm on anyone else.

Shaykh Ibn Baaz said: “As for lying to one’s mother or father, it is impermissible. Rather, it is incumbent on you to be keenly truthful and mindful of the way you talk to them and your attitude with them. You should strive to earn their satisfaction by all lawful means. However, if there is a situation when truthfulness would incur their anger and cause serious trouble between you and them, while lying would not incur harm on any person but help you earn their satisfaction, it then falls into the category of lying intended for reconciliation between people. There is no sin on your part if you have to resort to this kind of lying due to necessity, as it falls into the category of lying intended for reconciliation between people as long as it does not harm any person and only helps you earn the pleasure of your parents, avoid angering them, and escape their insults.” [End of quote]

Allah Knows best.