Hadithcore
Sunan Abi Dawud, 4400
sahih· Al-Albani

A similar tradition has also been transmitted by al-A’mash through a different chain of narrators. He also said :

“... . Till he reaches puberty , and a lunatic till he is restored to consciousness.” ‘Umar then began to utter: Allah is most great.

حَدَّثَنَا يُوسُفُ بْنُ مُوسَى، حَدَّثَنَا وَكِيعٌ، عَنِ الأَعْمَشِ، نَحْوَهُ وَقَالَ أَيْضًا حَتَّى يَعْقِلَ ‏.‏ وَقَالَ وَعَنِ الْمَجْنُونِ حَتَّى يُفِيقَ ‏.‏ قَالَ فَجَعَلَ عُمَرُ يُكَبِّرُ ‏.‏

References2 variants
In-Book Reference
Book 40, Hadith 50
English Reference
Book 39, Hadith 4386