Bulugh al-Maram, Book 15, Hadith 1424 (In-Book)

Abu Hurairah (RAA), narrated that The Messenger of Allah said, “A son cannot ever repay his parents what he owes them, unless he finds them in slavery, then buys them and emancipates them.” Related by Muslim.

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ " لَا يَجْزِي وَلَدٌ وَالِدَهُ, إِلَّا أَنْ يَجِدَهُ مَمْلُوكًا فَيُعْتِقَهُ" } رَوَاهُ مُسْلِم ٌ 1‏.‏ ‏1 ‏- صحيح.‏ رواه مسلم ( 1510 )‏ وزاد: "فيشتريه" بعد قوله: "مملوكا".‏

sunnah.com

also referenced under: Book 15, Hadith 1468 (English)