The Book of Prayer
Bulugh al-Maram #447
كتاب الصلاة
وَلِلْخَمْسَةِ - وَصَحَّحَهُ اِبْنِ حِبَّانَ -: «صَلَاةُ اَللَّيْلِ وَالنَّهَارِ مَثْنَى مَثْنَى» وَقَالَ النَّسَائِيُّ: «هَذَا خَطَأٌ».
The Khamsah reported it - graded Sahib (authentic) by Ibn Hibban - with the wording:
“the (voluntary) day and night prayers are two Rak'at, two Rak'at (in pairs).”
an-Nasa'i said, “This is a mistake.”
وَلِلْخَمْسَةِ - وَصَحَّحَهُ اِبْنِ حِبَّانَ - : "صَلَاةُ اَللَّيْلِ وَالنَّهَارِ مَثْنَى مَثْنَى" وَقَالَ النَّسَائِيُّ : "هَذَا خَطَأٌ" .
"the (voluntary) day and night prayers are two Rak'at, two Rak'at (in pairs)." an-Nasa'i said, "This is a mistake."
— Bulugh al-Maram, Hadith 447