كتاب الحج
15  
The Book of Pilgrimage
(88)
Chapter: Al-Madinah eliminates its Dross and it is also called Tabah, and Taibah
(88)
باب الْمَدِينَةِ تَنْفِي شِرَارَهَا ‏‏
Sahih Muslim 1382 b

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 .
Reference : Sahih Muslim 1382b
In-book reference : Book 15, Hadith 558
USC-MSA web (English) reference : Book 7, Hadith 3190
  (deprecated numbering scheme)