Al-Hasan reported: Ibn Mas’ud, may Allah be pleased with him, said, “The death of a scholar is a loss that cannot be replaced for as long as the day and night alternate.”
Source: Shu’ab al-Imān 1590
عَنِ الْحَسَنِ قَالَ قَالَ ابْنُ مَسْعُودٍ رضي الله عنه مَوْتُ الْعَالِمِ ثُلْمَةٌ لَا يَسُدُّهَا شَيْءٌ مَا اخْتَلَفَ اللَّيْلُ وَالنَّهَارُ
1590 شعب الإيمان