Al-Kāfi

Hadith 1681
fear-of-god
9ـ عَنْهُ عَنِ ابْنِ فَضَّالٍ عَنْ يُونُسَ بْنِ يَعْقُوبَ عَنْ سَعِيدِ بْنِ يَسَارٍ بَيَّاعِ السَّابِرِيِّ قَالَ قُلْتُ لأبِي عَبْدِ الله (عَلَيهِ السَّلام) إِنِّي أَتَبَاكَى فِي الدُّعَاءِ وَلَيْسَ لِي بُكَاءٌ قَالَ نَعَمْ وَلَوْ مِثْلَ رَأْسِ الذُّبَابِ.
9. It is narrated from him (narrator of the Hadith above) from ibn Faddal from Yunus ibn Ya’qub from Sa’Id ibn Yasar Bayya’ al-Sabiri who has said the following: “Once I said to Abu ‘Abdillah (a.s.) ‘In my prayer I can only make a weeping-like face, but weeping does not come through.’ The Imam said, ‘Yes, even (tears) of the size of the head of a fly (are very good).”’
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī