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