Abu Hurairah (radiyAllaahu anhu) said: The Messenger of Allaah (sallAllaahu alayhi wasallam) said: "Indeed Allaah (the Mighty and Majestic) raises the station of the righteous slave in Paradise and he (the slave) will say, 'O Lord, how has this come to me?', and He will say, "Due to your son seeking forgiveness for you."
The hadeeth is saheeh
and is reported by Ibn Maajah, and al-Albaanee (rahimahullaah) declared it saheeh in as-Saheehah (no. 1597).
1. An indication that the supplication of a son for his father for forgiveness benefits him after his death, especially when the father is righteous.
2. An indication that a person's rank in Paradise can be increased on account of action besides his own, such as through the intercession of others, or his son seeking forgiveness for him.
- Saheeh al-Ahaadeeth al-Qudsiyyah by Ahmad Ramadhaan, Dar Ibn Hazm, 1st edition, 2010, (p. 190)