He said that Mu’adh would pray the evening prayer along with the Prophet, then return to his people and lead them in the evening prayer, it being a supererogatory prayer for him…* transmitted it. * The source is not mentioned. In <i>al-Masabih</i>, where the division of the chapters is into traditions which are <i>sahih</i> and traditions which are <i>hasan</i>, the collection of Tradition from which they are taken is not mentioned, but all those in section I are meant to be taken from Bukhari, or Muslim, or both. I have failed to find this one anywhere. The concordance does not seem to refer to it.

وَعَنْهُ قَالَ: كَانَ مُعَاذٌ يُصَلِّي مَعَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ الْعِشَاءَ ثُمَّ يَرْجِعُ إِلَى قَوْمِهِ فَيُصَلِّي بِهِمُ الْعِشَاءَ وَهِيَ لَهُ نَافِلَة. أخرجه الشَّافِعِي فِي مُسْنده والطَّحَاوِي وَالدَّارَقُطْنِيّ وَالْبَيْهَقِيّ