This hadith has been narrated by Yabya b. Sa'id with the same chain of transmitters (and the words are):" Just as a furance removes impurity," but no mention is made of iron.
وَحَدَّثَنَا عَمْرٌو النَّاقِدُ، وَابْنُ أَبِي عُمَرَ، قَالاَ حَدَّثَنَا سُفْيَانُ، ح وَحَدَّثَنَا ابْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الْوَهَّابِ، جَمِيعًا عَنْ يَحْيَى بْنِ سَعِيدٍ، بِهَذَا الإِسْنَادِ وَقَالاَ " كَمَا يَنْفِي الْكِيرُ الْخَبَثَ " . لَمْ يَذْكُرَا الْحَدِيدَ .
Muslim
The Book of Pilgrimage • Hadith 558