Hadith 4:165
Abu Mas'ud al-Ansari said God’s messenger forbade that the imam should stand on anything when the people were behind him, meaning on a lower level than he was. Daraqutnl transmitted it in al-Mujtaba in Kitab al-jana’iz .
وَعَنْ أَبِي مَسْعُودٍ الْأَنْصَارِيِّ قَالَ: نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنْ يَقُومَ الْإِمَامُ فَوْقَ شَيْءٍ وَالنَّاسُ خَلْفَهُ يَعْنِي أَسْفَلَ مِنْهُ. رَوَاهُ الدراقطني وَأَبُو دَاوُد
Original Reference: Mishkat al-Masabih 1692