Imam Ali (a.s) said: “Being honest is a part of faith, and one who is honest will not even say useful lies, and will not say anything beyond his knowledge.”
وقال أيضا (عليه السلام): إن من حقيقة الإيمان أن يؤثر العبد الصدق حتى نفر عن الكذب حيث ينفع، ولا يعد المرء بمقالته علمه.
Similar narrations
Nahj al-Balāgha #2249458. Amīr al-mu’minīn, peace be upon him, said: Belief means that you should prefer truth (even) when it harms you rather than falsehood...
Mīzān al-Ḥikma #4334Imam Ali (AS) said, ‘Faith is to prefer to tell the truth, even if it be to your detriment, over lying even though it be to your benefit.