488. hadíth
وَ سُئِلَ: مَتَى تَجِبُ اَلصَّلاَةُ عَلَيْهِ قَالَ «إِذَا عَقَلَ اَلصَّلاَةَ وَ كَانَ اِبْنَ سِتِّ سِنِينَ.
He was asked : "When does the funeral prayer become obligatory for a child?" Imam (a.s) replied: "When the child understands the concept of prayer and is six years old."