In the name of Allah, the Most Compassionate, the Most Merciful.

Book of Testimony
Chapter: Those whose testimony is admissible

Any person who is free, Muslim, of legal maturity, who performs the prescribed duties and knows what nullifies them, from whom no major sin or flagrant injustice has appeared, who is not known for habitual lying and is generally regarded as truthful—such a person is counted upright (ʿadl) and his testimony is accepted, provided that by his testimony he is neither warding off liability from himself, nor drawing benefit to himself, nor venting personal spite.

Some of our authorities add that uprightness requires a man to be pleasing and trustworthy, balanced in his conduct, known for purity and avoidance of base acts, cautious about associating with people of ill character, and scrupulous in his dealings.

If an upright witness becomes suspect, his testimony is rejected, in keeping with the report: “The testimony of a litigant or of one under suspicion is not accepted.”