Abu Muslim al-Khawlani reported: A man came to him and he said, “Instruct me, O Abu Muslim.” Abu Muslim, may Allah have mercy on him, said, “Remember Allah under every tree and hillside.” The man said, “Tell me more.” Abu Muslim said, “Remember Allah until people think you have gone mad with the remembrance of Allah.” Abu Muslim used to frequently mention Allah. A man saw him mentioning Allah and he said, “Has this companion of yours gone mad?” Abu Muslim heard him and he said, “This is not madness, O son of my brother, rather this is the cure for madness.”
Source: Shu’ab al-Imān 685
عَنْ أَبِي مُسْلِمٍ الْخَوْلَانِيِّ أَنَّ رَجُلًا أَتَاهُ قَالَ لَهُ أَوْصِنِي يَا أَبَا مُسْلِمٍ قَالَ رحمه الله اذْكُرِ اللهَ تَحْتَ كُلِّ شَجَرَةٍ وَحَجَرٍ قَالَ زِدْنِي فَقَالَ اذْكُرِ اللهَ حَتَّى يَحْسِبَكَ النَّاسُ مِنْ ذِكْرِ اللهِ مَجْنُونًا قَالَ فَكَانَ أَبُو مُسْلِمٍ يُكْثِرُ ذِكْرَ اللهِ فَرَآهُ رَجُلٌ يَذْكُرُ اللهَ فَقَالَ أَمَجْنُونٌ صَاحِبُكُمْ هَذَا فَسَمِعَهُ أَبُو مُسْلِمٍ فَقَالَ لَيْسَ هَذَا بِالْجُنُونِ يَا ابْنَ أَخِي وَلَكِنْ هَذَا دَوَاءُ الْجُنُونِ
685 شعب الإيمان