A hadith like this has been reported on the authority of Nafi` with the same chain of transmitters (and the words are):
"I think Ibn `Umar said: The seventieth part from Prophecy." (FR)
Reference (FR): Sahih Muslim 2265 c (FR)
In-book reference (FR): Book 42, Hadith 22 (FR)
USC-MSA web (English) reference(deprecated numbering scheme): Book 29, Hadith 5634 (FR)