Al-Hafiz, in al-Isabah (3/88), also attributed this hadith to al-Hasan ibn Sufyan and al-Baghawi, through Ibn Lahiah. Al-Suyuti attributed it to Ahmad and al-Tabarani in al-Kabir. Yet I have not found it in Ahmad’s Musnad—which is what is intended when a report is attributed to him without qualification. Indeed, this Sad ibn al-Mundhir is not mentioned in the Musnad. It is found in al-Tabarani (5481) through another route from Ibn Lahiah. The following hadith likewise supports recitation in three days.

1513 — “Complete the recitation of the Quran once each month; complete it in twenty-five days; complete it in twenty days; complete it in fifteen days; complete it in seven days. Whoever recites it in fewer than three days will not comprehend it.”

Imam Ahmad recorded it (2/165 and 189) through Hummam, from Qatadah, from Yazid ibn Abdullah ibn al-Shikhkhir, from Abdullah ibn Amr, who said: “I said, ‘O Messenger of Allah, in how many days should I recite the Quran?’ He said, ‘Recite it in a month.’ I said, ‘I am capable of more than that.’ He said, ‘Recite it in twenty-five days.’ I said …” the hadith.

Abu Dawud recorded it in abbreviated form, and al-Tayalisi recorded its final sentence. See Sahih Abi Dawud (1257).

The hadith has many routes of transmission in the Musnad, both in full and in abbreviated form. Among them is what Ahmad recorded (2/188 and 195) through Shubah, from Amr ibn Dinar, from Abu al-Abbas, from Abdullah ibn Amr, who said: The Messenger of Allah, peace and blessings be upon him, said to me: “Recite the Quran in a month.” I said, “I can manage more than that,” and I continued to ask him until he said, “Recite the Quran in five days.”