Mustadrak al-Hakim 726 — On the virtue of the five prayers

Amr bin Shu'ayb narrates from his father, from his grandfather (Sayyiduna Abdullah bin Amr), that the Messenger of Allah (peace and blessings be upon him) said: "Command your children to pray at the age of seven, beat them for (abandoning) it at the age of ten, and separate their beds."
Imam al-Hakim says that Yahya bin Ma'in declared Amr bin Shu'ayb trustworthy, and Imam Ishaq bin Rahawayh said that if the one narrating from Amr bin Shu'ayb is trustworthy, then this narration is as strong as Nafi' from Ibn Umar.

Yahya bin Ma'in says that Amr bin Shu'ayb is trustworthy.
Imam al-Hakim says that the imams criticised this chain only because of its being mursal (with a gap), since Shu'ayb did not hear directly from his grandfather Abdullah bin Amr.

Imam Ishaq bin Rahawayh says that if the narrator from Amr bin Shu'ayb is trustworthy, then this chain will be considered equal in reliability and strength to 'Ayyub from Nafi' from Ibn Umar'.