Ibn Hajar Al-Haythami said:
“If the enemy captures a single Muslim, it becomes wajib (obligatory) on everyone who has the ability to rush to their rescue (even without seeking anyone’s permission). It is apparent that it is compulsory on everyone, similar to the situation where the enemy invades our land. Moreover saving our brothers is of a higher priority, as the sanctity of a Muslim is greater (than the sanctity of a State).”
[Tuhfah Al-Muhtaj, 9/237]