Messenger of Allah (S) said: "Teach the boy Salat when he is seven years old, and beat him (if he does not pray) when he is ten."  

قَالَ رَسُولُ اللَّهِ ﷺ عَلِّمُوا الصَّبِيَّ الصَّلاَةَ ابْنَ سَبْعِ سِنِينَ وَاضْرِبُوهُ عَلَيْهَا ابْنَ عَشْرٍ قَالَ وَفِي الْبَابِ عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو