The Funeral Prayer (Salat Al-Janazah)
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 26
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 عليه السلام replied: "When the child understands the concept of prayer and is six years old."
- Ṣaḥīḥ al-Faqīh