is one of Muhammad's secretaries.
It is related that, when Muhammad instructed Abdullah to write down the words (Surah xxiii.12-14) ... Abdullah exclaimed, "And blessed be God, the best of creators"; and Muhammad told him to write that down also. Whereupon Abdullah boasted that he had been inspired with a sentence which the Prophet had acknowledged to be part of the Qur'an. It is of him that is written in the Qur'an, Surah vi.93, ... (Hughes' Dictionary, p. 2)This incident, of course, casts doubt on the inspiration of the Qur'an, when Muhammad so easily added to the words given.
More discussion in Sources of the Qur'an: Contributions by `Abdullah ibn Sa`d Ibn Abi Sarh