Prayer: The Eldest Son Being Underage or Insane at the Time of His Father's Death
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1377
If at the time of his father’s death the eldest son was not of the age of legal responsibility (bāligh) or he was insane, then when he becomes bāligh and/or sane, it is not obligatory for him to perform his father’s qaḍāʾ prayers.