Qur'an, An-Nisa, Surah 4:135
Believers, uphold justice. Always bear true witness, even if it be against yourself, your parents, or your relatives—and regardless of whether the person against whom you are speaking is rich or poor. God is close to people regardless of their material circumstances. Do not be led by emotion, as this may cause you to swerve from the truth. If you distort your testimony, or refuse to testify, remember that God is aware of all your actions.