The Ruling on Swearing by the Prophet (peace and blessings be upon him)

Is swearing by the Prophet (peace and blessings be upon him) an oath that requires expiation? And if it is not, what is the penalty for the one who swears by this oath?

Answer: It is not permissible to swear by other than Allah not by the Prophet, nor by anyone else, and an oath is not valid by other than Allah, nor is an expiation obligatory for it; because the Prophet (peace and blessings be upon him) said: agreed upon by al-Bukhari and Muslim, and because he (peace and blessings be upon him) said: narrated by Imam Ahmad, Abu Dawud, and al-Tirmidhi with a sound chain.
The one who swears by other than Allah must repent to Allah from that with sincere repentance; and that is by ceasing to swear by other than Allah, feeling remorse for what has passed of that, and having the sincere determination not to return to swearing by other than Allah; due to the saying of His Lord (Glorified and Exalted is He): the verse [al-Tahrim: 8], and what has come in its meaning from verses and hadiths. And success is from Allah.