The Messenger of Allah ﷺ said, "Whoever recites a single letter from the Book of Allah receives a good deed for it, and each good deed is multiplied tenfold. I do not say that Alif Lam Mim is one letter, rather Alif is a letter, Lam is a letter, and Mim is a letter."
قال رسول الله ﷺ: من قرأ حرفا من كتاب الله فله به حسنة، والحسنة بعشر أمثالها، لا أقول {الم} حرف، ولكن ألف حرف، ولام حرف، وميم حرف.
Tirmidhi (2910) narrated it from Muhammad bin Bashshar, who said, Abu Bakr Hanafi (whose name is Abdul-Kabir bin Abdul-Majid) narrated to us, who said, Dahhak bin Uthman narrated to us, from Ayub bin Musa (that is, the Umawi), who said, I heard Muhammad bin Kaab Qurazi say, I heard Abdullah bin Masud say, and then he mentioned it. Its chain of transmission is hasan because of Dahhak bin Uthman, for his hadith is hasan. Tirmidhi said, "This is a hasan sahih hadith, gharib from this angle," and he said, "This hadith is also reported through a different route from Ibn Masud. Abu Ahwas narrated it from Ibn Masud, some raising it to the Prophet and some stopping it at Ibn Masud."Similar in meaning is what was reported from Awf bin Malik Ashjai, who said that the Messenger of Allah ﷺ said, "Whoever recites a letter of the Quran, a good deed is recorded for him, and I do not mean that "Alif Lam Meem. This is the Book" [Baqarah 2:1–2] counts as one letter, but rather the alif is a letter, the lam is a letter, the meem is a letter, the dhal is a letter, another lam is a letter, and the kaf is a letter." This was narrated by Bazzar (2761) and Tabarani in al-Kabir (1/76) and al-Awsat (316), all of them through various routes from Musa bin Ubayda Rabazi, from Awf bin Malik Ashjai, and then he mentioned it. Musa bin Ubayda Rabazi is daif by the unanimous agreement of the scholars. He added to the hadith, "and the dhal is a letter, the lam is a letter, and the kaf is a letter."As for what was reported from Abu Dharr, raised to the Prophet, "You must recite the Quran and remember Allah, for it is a light for you on earth and a treasure stored up for you in heaven," this is daif. Ibn Hibban narrated it (361) within a long hadith, and its chain contains Ibrahim bin Hisham bin Yahya bin Yahya Ghassani. Dhahabi said in al-Mizan, He is the one behind the long hadith of Abu Dharr, which he alone transmitted from his father, from his grandfather. He quoted from Abu Hatim, He is a liar, and quoted from Ibn Jawzi that Abu Zura said, He is a liar.I say, this portion of the hadith has many corroborating reports, but it has not been established as sahih from Abu Dharr.