Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Messenger of Allah (peace and blessings be upon him) said: "When your children reach seven years of age, teach them to pray; punish them for not praying at the age of ten; and separate their sleeping places. And when one of you marries his slave-girl to his servant or hired worker, then let her not look at his awrah, and the awrah is between the navel and the knees."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3235