Is Salah (Prayer) valid if offered

Q 4: if I am offering Tahiyyat-ul-Masjid (two-unit Prayer to salute the mosque) or Nafilah (supererogatory) prayer and someone else joins me thinking that I am offering the obligatory Salah, what should I do in this case?

A: It is permissible according to the most preponderant opinion of the scholars for a person offering the obligatory Salah to be led by a person offering a supererogatory Salah. He may also join a person who has commenced Salah alone. The Imam in this case should not prevent anyone from joining him in Salah. It is authentically reported that Ibn `Abbas (may Allah be pleased with him) came to the Messenger of Allah (peace be upon him) while he was offering Salah alone at night. He stood by his left side, thereupon, the Prophet (peace be upon him) pulled him to his right side and led him in Salah. It is also authentically reported that Mu`adh (may Allah be pleased with him) used to offer the `Isha' (Night) Salah with the Messenger of Allah (peace be upon him) then lead his people in the same Salah. The Prophet (peace be upon him) did not disapprove of this. The Prophet (peace be upon him) led a group of his Companions in performing two Rak`ahs of Salat Al-Khawf (Prayer in Times of Fear) and pronounced the Taslim (salutation of peace ending the Prayer). Afterwards, he led the other group in performing two Rak`ahs and pronounced the Taslim. Related by Abu Dawud. The second Salah offered by the Prophet (peace be upon him) was Nafilah (supererogatory) payer.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.