What is the Muslim's duty when he sees someone hit a parked car and flee: should he wait for the owner of the damaged car to give him the license plate number of the car that caused the accident, or should he leave?

If someone witnesses an accident and no one else sees it, they must bear witness in order to protect the rights of the car owner, either by waiting for them or leaving contact information. If the accident occurs in front of a group, bearing witness becomes a communal obligation (fard kifayah). Bearing and rendering testimony is a communal obligation, unless there is no one else available, in which case it becomes an individual obligation. There is no sin upon the witness if they suffer harm or if their testimony is not beneficial. If someone knows of a testimony and is not asked to give it, then: if it pertains to the rights of Allah, it falls into two categories: that which does not entail continuous prohibition, like adultery, in which case it should be concealed; and that which entails continuous prohibition, like divorce, in which case informing is obligatory. If it pertains to the rights of a human being, then informing the rights-holder is obligatory. There is a difference of opinion regarding praising or blaming someone who testifies without being asked. The correct view is that if the rights-holder is unaware of the testimony, it is preferable to testify, otherwise not. If someone sees a person committing a sin that relates to the rights of people, it is incumbent upon them to inform the rights-holder and give testimony if necessary, unless they fear harm.