The Prophet ﷺ commanded him to complete reading the Quran in forty days, then in a month, then in twenty days, then in fifteen, then in ten, then in seven. He said, "It ended at seven."
أمره النبي ﷺ أن يقرأ في أربعين، ثم في شهر، ثم في عشرين، ثم في خمسة عشر، وفي عشر، ثم في سبع قال: انتهى إلى سبع.
Nasai narrated it in Al-Kubra (8015) from Zakariya bin Yahya, who said, Muhammad bin Ubayd bin Hassab told us, who said, Muhammad bin Thawr told us, from Mamar, from Simak bin Fadl, from Wahb bin Munabbi, from Amr bin Shuayb, and he related it. Its chain is hasan because of Amr bin Shuayb.Abu Dawud (1395) and Tirmidhi (2947) also narrated it, both by way of Mamar, from Simak bin Fadl, from Wahb bin Munabbi, from Abdullah bin Amr, who related something similar. However, Tirmidhi limited it to his saying, "Recite the Quran in forty." He said, this is a hasan gharib hadith. Some narrators reported from Mamar, from Simak bin Fadl, from Wahb bin Munabbi, that the Prophet ﷺ commanded Abdullah bin Amr to recite the Quran in forty.I say, this chain contains a break, for Wahb bin Munabbi did not hear it directly from Abdullah bin Amr, as Nasai stated in Al-Kubra. He then narrated it through an intermediary, Amr bin Shuayb, which connects the chain, making it hasan, as I have said.Many of the early scholars held it disliked to complete a full recitation of the Quran in less than three days. In the Sunan of Saeed bin Mansur (2/442), it is reported from Ibn Masud, as his own statement, "Do not recite the Quran in less than three days." Abdullah bin Masud used to complete the Quran every three days, and rarely made use of the daytime for it. Ubayy bin Kaab used to complete the Quran in eight days. Muaz disliked reciting the Quran in less than three days. Likewise, many of the successors held this view, and it is the position chosen by Ahmad and Ishaq and others.Ayesha criticized one who recited the whole Quran in a single night, once or twice, as mentioned in the hadith that follows.