because Abu Salamah, given his age, could not have met Abdullah ibn Masud or received it from him.”
I say: In the chain of Layth’s route is Abdullah ibn Salih, who is weak on account of his memory. Therefore, Haywah’s narration is more authentic, but it is disconnected for the reason mentioned by al-Tahawi: Abu Salamah did not hear from Ibn Masud. Ibn Masud died in 32 AH, the same year in which Abd al-Rahman ibn Awf—the father of Abu Salamah—died. The scholars have stated that Abu Salamah did not hear from his father because he was too young. Thus, this is the hidden defect in the hadith: the disconnection.
I have found another connected route for it, narrated by Falfalah al-Hanafi, who said: “I was among those who rushed in alarm to Abdullah—meaning Ibn Masud—concerning the codices. We entered upon him, and a man from the people said: ‘We have not come to you as visitors; rather, we have come because this report has alarmed us.’ He said: ‘The Quran was sent down to your Prophet through seven gates, in seven modes, whereas the earlier Scripture used to be sent down through one gate, in one mode.’” It was recorded by al-Tahawi (4/182) and Ahmad (1/445).
I say: This is a good, connected chain. All its narrators are recognized as trustworthy, except for this Falfalah, whose father’s name was Abdullah. Ibn Abi Hatim mentioned him (3/2/92–93), without recording either criticism or accreditation of him. Ibn Hibban included him among the trustworthy Successors (1/185), and a number of trustworthy narrators related from him, as stated in al-Tahdhib. It is possible that this Falfalah was the intermediary in the transmission of this hadith between Abu Salamah and Ibn Masud.
In sum, this hadith is good in my view by virtue of this route. And Allah knows best. It has also been narrated from Abu Hurayrah, but its chain is extremely weak and is not suitable for corroboration. Its beginning contains an addition, which I cited on its account in the other book (1346).