Musnad Ahmad 30:3479

Yazid narrated to us, Hammad ibn Salamah informed us, from ‘Asim ibn Abi al-Najud, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, Allah the Almighty and Majestic raises the degree of the righteous servant in Paradise, so he says: 'O my Lord, how did I attain this?' He says: 'By your child’s seeking of forgiveness for you.'"