Virtues of Optional Prayers in Islam
Question

What is the excellence of optional prayers?
Praise be to Allah.The virtues of offering optional prayers in Islam are mentioned in many hadiths:

The mother of the faithful, Umm Habibah Ramlah bint Abu Sufyan, narrated  that she heard the Prophet (peace and blessings of Allah be upon him) saying: “A house will be built in paradise for every Muslim who offers twelve rak`ahs of optional prayer other than the obligatory prayer in a day and night, to seek the pleasure of Allah.” (Narrated by Muslim)

Note: These extra 12 rak`ahs of optional prayers , according to Imam An-Nasai and at-Tirmidhi are: 2 rak`ahs before the obligatory prayer of early morning (Fajr), and 4 rak`ahs before (Zuhr) and 2 rak`ahs after it ,and 2 rak`ahs after the obligatory prayer of early evening prayer (Magrib) and 2 rak`ahs after the obligatory prayer of night (`Isha) prayer.

Abu Hurairah (may Allah be pleased with him) said: “My friend, the Prophet (peace and blessings of Allah be upon him) advised me to observe three things and I shall not leave them till I die: 1. “To observe fasting three days every (lunar) month; 2.” To offer the Duha prayer ; 3. To offer Witr prayer before sleeping.” (Narrated by al-Bukhari and Muslim)
`Aishah (may Allah be pleased with her) narrated that the Prophet (peace and blessings of Allah be upon him) said: “The two rak`ahs before dawn (Fajr) prayer are better than the world and all that it contains.” (Narrated by Muslim)
`Aishah (may Allah be pleased with her) narrated that the Prophet (peace and blessings of Allah be upon him) was never more regular and strict in offering any voluntary prayers than the two rak`ahs (sunnah before) dawn (Fajr) prayer. (Narrated by Al-Bukhari and Muslim)
Umm Habibah (may Allah be pleased with her) narrated that the Prophet (peace and blessings of Allah be upon him) said: “Whoever observes the practice of offering four rak`ahs before Zuhr prayer and four rak`ahs after it. Allah will shield him against the fire of hell.” (Narrated bay Abu Dawud and At-Tirmidhi)
One should make Witr as the last prayer (prayer) (at night).

‘Abdullah bin ‘Umar (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) said: “Make Witr as your last prayer (prayer) at night.” (Narrated by Al-Bukhari and Muslim)

If anyone enters a mosque, he should offer two rak`ah before sitting.

Abu Qatada (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) said: “If any one of you enters a mosque, he should pray two rak`ahs before sitting.” (Narrated by Al-Bukhari and Muslim)

Abu Hurairah (may Allah be pleased with him) narrated that Allah’s Messenger (peace and blessings of Allah be upon him) said to Bilal (may Allah be pleased with him) “Tell me about the most hopeful act (i.e. one which you deem the most rewarding with Allah) you  have done since your acceptance of Islam because I heard the sound of the steps of your shoes in front of me in Paradise.” Bilal said: “I do not consider any act more hopeful than that whenever I make  ablution (wudu) at any time of night or day, I offer prayer (prayer) for as long as was destined for me to offer.” (Narrated by Al-Bukhari and Muslim)  

And Allah knows best.