Born in Jerusalem, he belonged to the Rechabites, and was one of the apostles of the Karaites who traveled extensively to win new adherents for Karaism and thereby strengthen the failing faith of their coreligionists.
He often reproaches the Rabbinites for preaching and teaching for the sake of gain, asserting that their aims are not as free from selfishness as those of the Karaites.
Sahl's polemics throw much light upon the degree of laxness in religious ceremonial prevalent in his time.
Thus he complains against the Rabbinites that in many matters they openly made common cause with non-Jews and were thereby led astray from the strict observance of the dietary laws.
Sahl was especially interested in calendric questions, and in one of his writings reviews the whole controversy between Rabbi Meïr of Jerusalem and Saadia in order to draw attention to the conciliatory disposition of the Palestinian Jews.