"Whoever turns away from the reminder of the Merciful, we will assign to him a devil, who will be a partner to him." [(43): 36]
The reminder is the reminder with which He sent His Messenger such as the Qur'aan. So, whoever does not believe in the Qur'aan, and all the information contained therein, has turned away from it, and so is assigned a shaitaan. He turns himself as blind from the Book of Allah and Allah will turn him blind on the Day of Judgment:
"And whoever turns away form my reminder will have an oppressive, restricted life, and We will resurrect him on the Day of Qiyamah: blind. He will say: "Oh my Lord! Why have you resurrected me blind, while I used to see?" (Allah) will say: "Just as My verses came to you and you forgot them, today you are forgotten." [Soorah Ta-Ha (20): 124-126
"And whoever turns away form my reminder will have an oppressive, restricted life, and We will resurrect him on the Day of Qiyamah: blind. He will say: "Oh my Lord! Why have you resurrected me blind, while I used to see?" (Allah) will say: "Just as My verses came to you and you forgot them, today you are forgotten." [Soorah Ta-Ha (20): 124-126
The Prophet (ﷺ) said, “Whoever guides someone to goodness will have a reward like one who did it.”
( Ṣaḥīḥ Muslim)
The Prophet (ﷺ) said, "Convey (my teachings) to the people even if it were a single verse."
( Saheeh Bukhari)
The Prophet (ﷺ) said, "By Allah, that Allah guides a man through you is better for you than a herd of expensive red camels."
(Ṣaḥīḥ al-Bukhārī)
The Prophet (ﷺ) said, "When the human being dies, his deeds end except for three: ongoing charity, beneficial knowledge, or a righteous child who prays for him."
(Ṣaḥīḥ Muslim).