How to Distinguish Between the Sunnah and Custom in the Actions of the Prophet?

Question:
How do we distinguish between an action of the Prophet (peace and blessings be upon him) that is a Sunnah and one that is a custom?

Answer:
The original rule is that his actions (peace and blessings be upon him) are Sunnah; this is the original rule [Al-Ahzab: 21] except for what is known through other evidence that the believer recognizes as ordinary matters in which the Prophet (peace and blessings be upon him) did not command anything and did not persist in them, such as types of food, types of clothing, and the like, in which the Prophet (peace and blessings be upon him) did not persist, indicating that they are ordinary matters. Similarly, the issue of growing or shaving the head, and wearing a shirt or an izar and rida.
Q: Who said that an action that does not result in reward, prohibition, or command is a custom?
The Shaykh: The original rule is to follow the example of the Prophet (peace and blessings be upon him), except for ordinary matters in which he (peace and blessings be upon him) did not persist. These are ordinary matters, sometimes he does them and sometimes he leaves them off, such as clothing and the like, types of food, and the like.
Q: And is there reward for adopting these customs?
The Shaykh: Allah knows best.