And from [part of] the night, pray with it as additional [worship] for you; it is expected that your Lord will resurrect you to a praised station. Qur’an 17:79 
Narrated Abu Huraira(R): Allah's Messenger (May Allah Honour him and Grant him Peace) said, "Allah said, 'I will declare war against him who shows hostility to a pious worshipper of Mine. And the most beloved things with which My slave comes nearer to Me, is what I have enjoined upon him; and My slave keeps on coming closer to Me through performing Nawafil (praying or doing extra deeds besides what is obligatory) till I love him, so I become his sense of hearing with which he hears, and his sense of sight with which he sees, and his hand with which he grips, and his leg with which he walks; and if he asks Me, I will give him, and if he asks My protection (Refuge), I will protect him; (i.e. give him My Refuge) and I do not hesitate to do anything as I hesitate to take the soul of the believer, for he hates death, and I hate to disappoint him." Sahih Al-Bukhari Vol 8: 509 (6502 NE)
Umm Habiba (the wife of the Prophet) reported Allah's Messenger (May Allah Honour him and Grant him Peace) as saying: A house will be built in Paradise, for anyone who prays in a day and a night twelve rak'ahs; and she added: I have never abandoned (observing them) since I heard it from the Messenger of Allah (may peace be upon him). Some of the other narrators said the same words: I have never abandoned (observing them) since I heard (from so and so). Sahih Muslim 728 a (Book 4, Hadith 1579 NE)
He who observed twelve voluntary rak'ahs, a house will be built for him in Paradise. Sahih Muslim 728 b (Book 4, Hadith 1580 NE) Sunan Nasai Vol 2: 1811 
Besides the prescribed obligatory prayers, a person may come up with as many voluntary prayers as is possible. Through voluntary prayers a person receives additional rewards and through them he draws closer to Allah (subhanahu wa ta'ala) although a person will not be punished for neglecting to perform voluntary prayers.
However, the Prophet (peace be upon him) had set a tradition of practicing certain voluntary prayers before and/or after the obligatory prayers and every Muslim is strongly recommended to perform them. These are as follows: