Fasting: Obligatory Fasts Other Than Ramadan of a Deceased Father
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1682
If a father had not kept obligatory fasts other than the fasts of the month of Ramadan – for example, he had not kept a fast that had become obligatory on account of a vow – or, if he had been hired to fast on behalf of someone else but had not done so, it is not obligatory for the eldest son to make up such fasts.