Offering supererogatory Salahs during prohibited times

Q 6: Hadith have been reported including that narrated by Ibn `Umar (may Allah be pleased with both) who said, I memorized (a tradition of) ten Rak`ahs (units of prayer) of Nawafil (supererogatory prayers) from the Prophet (peace be upon him): two Rak`ahs before Zhuhr (Noon) Prayer and two after it; two Rak`ahs after Maghrib (Sunset) Prayer in his house, and two Rak`ahs after `Isha' (Night) Prayer in his house, and two Rak`ahs before Fajr (Dawn) Prayer. Related by Al-Bukhari. It is also narrated on the authority of Um Habibah bint Abu Sufyan that the Prophet (peace be upon him) stated, Whoever prays twelve Rak`ahs of prayer voluntarily in a day and night, Allah will build him a house in Jannah (Paradise). These twelve Rak`ahs are: Four Rak`ahs before the Zhuhr (Noon) Prayer and two Rak`ahs after it, two Rak`ahs after Magrib (Sunset) Prayer, two Rak`ahs after `Isha (Night) Prayer and two Rak`ahs before the Fajr (Dawn) Prayer. Related by Al-Tirmidhy, and he said: This is a Hasan (sound) and authentic Hadith.Are the two Rak`ahs of Tahiyyat-ul-Masjid included among the Rak`ahs mentioned in the two Hadith? Do the two supererogatory Rak`ahs after `Isha' Prayer the two Shaf` Rak`ahs (two units of Prayer, particularly before the final unit of the odd-number prayer)?

A: The regular supererogatory Salah performed before the obligatory Salah serve as Tahiyyat-ul-Masjid (two-unit-Prayer to greet the mosque), because it is important for the Muslim not to sit in the Masjid before performing Salah. So, if he offers the regular supererogatory Salah, it will be sufficient for him. The same applies when entering the Masjid and the congregational Salah has already begun. In this case there is no need to offer the two Rak`ahs of Tahiyyat-ul-Masjid as the obligatory Prayer will count for it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.