Tafsir of Sad 38:86

(of any reward) Meaning: any worldly reward, whether great or small.

(And I am not of the pretenders) Meaning: not of those who feign and adorn themselves with that which they do not possess. You have never known me to be characterized by or to claim what I do not have, such that I would fabricate prophethood or forge the Quran. He, peace and blessings be upon him, was commanded to say this statement to them about himself, not to inform them of the content, but as an appeal to what they already knew of him, peace and blessings be upon him, and to remind them of what they had learned. In this, there is a condemnation of pretension (takalluf).

Ibn Adi recorded from Abu Barzah that he said: The Messenger of Allah, peace and blessings be upon him, said: "Shall I not inform you of the people of Paradise?" We said: "Yes, O Messenger of Allah." He said: "They are those who are merciful among themselves." He said: "Shall I not inform you of the people of the Fire?" We said: "Yes." He said: "They are the desperate, the hopeless, the liars, and the pretenders."

The sign of the pretender, as recorded by al-Bayhaqi in Shu'ab al-Iman from Ibn al-Mundhir, is three things: to challenge one who is above him, to strive for that which he cannot attain, and to speak of that which he does not know. In the Sahihayn, it is narrated that Ibn Mas'ud said: "O people, whoever among you has knowledge, let him speak of it, and whoever does not know, let him say 'Allah the Exalted knows best.'" Allah the Exalted said to His Messenger, peace and blessings be upon him: (Say: I ask of you no reward for it, and I am not of the pretenders).