It is narrated from Sayyiduna Anas (may Allah be pleased with him) that Sayyidah Zaynab (may Allah be pleased with her) emigrated to the Messenger of Allah (peace and blessings be upon him) while her husband was a disbeliever. Then the Muslims took Abu al-As bin al-Rabi' captive, and Sayyidah Zaynab (may Allah be pleased with her) said: I have granted protection to Abu al-As. So the Prophet (peace and blessings be upon him) upheld her protection and said: "Even the lowest-ranking individual among the Muslims may grant protection (to a disbeliever)."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19252