The regular supererogatory Salah

Q 3: It is well-known that Fajr (Dawn) Prayer is two Rak`ahs (unit of Prayer). One is recommended to perform two supererogatory Rak`ahs before Fajr Prayer. But I noticed that many people perform four Rak`ahs before Iqamah (call to start the Prayer) believing that the first two Rak`ahs are for Tahiyyat-ul-Masjid (two-unit Prayer to salute the mosque) and last two Rak`ahs a recommended supererogatory Salah. Is it permissible to do so? Are these two supererogatory Rak`ahs sufficient for Tahiyyat-ul-Masjid?

A: If one performs the two supererogatory Rak`ahs that are to be done before Fajr Prayer in the Masjid, then he is not required to perform Tahiyyat-ul-Masjid. But If he performs these two Rak`ahs at home and then comes to the Masjid, he is permitted to perform Tahiyyat-ul-Masjid before the announcement of Iqamah. However, if Iqamah is announced, he is not required to perform Tahiyyat-ul-Masjid.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.