[DongoSab]

If one needs to swear a false oath in order to save a person whose life is unlawful to take from being killed, then one must swear it, for saving such a person’s life is obligatory, and if doing so depends on an oath, it is obligatory.
Suwayd ibn Handhala (Allah be well pleased with him) said: “We set out to the Messenger of Allah (Allah bless him and give him peace) and Wa’il ibn Hajar was with us, and he was captured by an enemy. The group was forced to swear an oath [that all were of the same clan, which was under a protection agreement], so I swore that he was my brother, and they released him. We reached the Messenger of Allah (Allah bless him and give him peace) and I told him that the group had been forced to swear, and that I had sworn he was my brother, and he said, “You told the truth: the Muslim is the brother of the Muslim” (Abu Dawud, 3.224:3256. S).
Shaykh Nuh Keller in Adab of Islam.