A Muslim asked to provide testimony in a legal case must uphold the principle of truthfulness, as honesty is a core Islamic value. They should provide truthful testimony, considering the importance of justice and fairness. However, they should also weigh the potential harm or injustice that may result from their testimony. In such cases, they may seek guidance from religious scholars or legal counsel to balance their duty to truth with the possible consequences, ensuring that their actions align with both ethical obligations and Islamic teachings.