Sa'id became a Muslim not later than 614.

His wife Fatima was also an early convert. At first they kept their faith secret because Fatima's brother Umar was a prominent persecutor of Muslims. Khabbab ibn al-Aratt often visited their house and read the Qur'an to them.

One day Umar (RA) entered their house while Khabbab (RA) was reading and demanded to know what they were reading. When they denied that anything had been read, Umar seized Sa'id and knocked him to the floor. Fatima stood up to defend her husband, and Umar hit her so hard that she bled. The couple admitted that they were Muslims. At the sight of the blood, Umar was sorry for what he had done, and asked to see what they had been reading. It was Sura Ta-Ha, later to become the twentieth Surah of the Qur'an. Impressed by the beauty of the words, Umar decided to become a Muslim.