Al-Kāfi

Hadith 1427
certainty
2ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ عَلِيِّ بْنِ أَسْبَاطٍ عَنْ أَبِي إِسْحَاقَ الْخُرَاسَانِيِّ قَالَ كَانَ أَمِيرُ الْمُؤْمِنِينَ (عَلَيهِ السَّلام) يَقُولُ فِي خُطْبَتِهِ لا تَرْتَابُوا فَتَشُكُّوا وَلا تَشُكُّوا فَتَكْفُرُوا.
2. A number of our people have narrated from Sahl ibn Ziyad from Ali ibn Asbat from abu Ishaq al-Khurasani who has said the following: “Amir al-Mu’minin, Ali ibn abu Talib (a.s.) would say in his sermons, ‘Do not suspect; you will doubt and do not doubt; you will become unbelievers.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī