Arabic text
عن أبي هريرة رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : «لاَ يَجْزِي ولدٌ والدًا إلا أن يجده مملوكًا، فَيَشْتَرِيَهُ فَيُعْتِقَهُ».
Translation
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "No son can repay the kindness of his father unless he finds him a slave and buys him and emancipates him."
Explanation
The son can never repay his father for all the good he has done or fulfill all the rights his father has over him, except if the father was a slave and the son emancipated him by buying him (from his master) and setting him free.
Source: HadeethEnc.com