Which takes precedence: the Sunnah of the Prophet, peace and blessings be upon him, or the command of parents, if they conflict in a matter that is not sinful?

If the parents have a valid reason for preventing their son from performing supererogatory acts (sunnah (definition)), such as their need for him in service, then their obedience is obligatory. Otherwise, there is no obedience to them. It has been previously noted that continuous obedience to them in abandoning sunnah or obligatory acts without a valid reason may lead to the neglect of religious rituals. It is preferable for the son to combine adherence to the Sunnah with pleasing his parents, through good companionship, dutifulness, teaching them, and convincing them of what is good.