The Prophet ﷺ said, "A child cannot repay his father, unless he finds him enslaved and then buys him and sets him free."
حدثنا عبد الرزاق أنبأنا سفيان عن سهيل بن أبي صالح عن أبيه
عن النبي ﷺ قال لا يجزي ولد والده إلا أن يجده مملوكا فيشتريه فيعتقه
Its chain of transmission is sahih. Muslim reported it, 2/1148, no. 1510, in the Book of Manumission, the chapter on the merit of freeing one's father, with wording close to it. Abu Dawud reported it, 4/335, no. 5137, in the Book of Manners, the chapter on filial piety toward parents, with its exact wording. And Tirmidhi reported it, 4/315, no. 1906, in the Book of Righteousness, the chapter on what has been narrated regarding the rights of parents.