ʿUyūn akhbār al-Riḍā - Volume 1 > Various Traditions From al-Ridha (s)
Hadith #5

5 - وَبِهذَا الإِسناد عَنِ الرِّضا عَلَيْهِ السَّلامُ، عَن أَبيهِ مُوسَى بْنِ جَعْفَر عَلَيْهِ السَّلامُ قالَ: قِيلَ لِلصَّادِقِ‏ عَلَيْهِ السَّلامُ أَخْبِرْنَا عَنِ الطَّاعُونِ فَقَالَ: عَذَابُ اللَّهِ لِقَوْمٍ وَرَحْمَةٌ لآِخَرِينَ قَالُوا وَكَيْفَ تَكُونُ الرَّحْمَةُ عَذَاباً قَالَ: أَمَا تَعْرِفُونَ أَنَّ نِيرَانَ جَهَنَّمَ عَذَابٌ عَلَى الْكُفَّارِ وَخَزَنَةُ جَهَنَّمَ مَعَهُمْ فِيهَا فَهِيَ رَحْمَةٌ عَلَيْهِمْ.

30-5 According to the same documentation, it has been narrated on the authority of Al-Ridha (s), on the authority of his father Musa ibn Ja’far (s), “As-Sadiq (s) was asked about the plague. The Imam (s) said, ‘It is God’s punishment for some people and His Mercy upon others.’ They asked, ‘How could Punishment be Mercy?’ The Imam (s) said, ‘Don’t you know that the Fire of Hell is Punishment for the atheists but is God’s Mercy upon the Guardians of Hell.’”