Purity: Obligation of Salat al‑Mayyit (Prayer for the Deceased)

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 582:

It is obligatory to perform salat al‑mayyit for a Muslim who has died, and for every child who is considered a Muslim and has completed six years of age.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)