Sayyidah Umm Salamah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), narrated that when the Messenger of Allah (peace and blessings be upon him) set out as an emigrant, Sayyidah Zaynab bint Rasulullah (peace and blessings be upon him) asked Abu al-As bin al-Rabi' for permission to go to her father, and he gave her permission. So she came to the Messenger of Allah (peace and blessings be upon him). Then Abu al-As bin al-Rabi' followed her to Madinah and sent word to her: Obtain a guarantee of safety for me from your father. She put her head out of the door of her chamber while the Messenger of Allah (peace and blessings be upon him) was leading the people in the Fajr prayer, and Sayyidah Zaynab (may Allah be pleased with her) said: O people, I am Zaynab, and I have granted protection to Abu al-As. When the Messenger of Allah (peace and blessings be upon him) finished the prayer, he said: "I did not know of this until I heard it just now; and even the lowest-ranking of the Muslims may grant protection to someone."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19250