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." (AR)
Reference (AR): Sahih Muslim 2265 c (AR)
In-book reference (AR): Book 42, Hadith 22 (AR)
USC-MSA web (English) reference(deprecated numbering scheme): Book 29, Hadith 5634 (AR)