Reward for Tarawih
Question

What is the reward for Tarawih prayers?
Praise be to Allah.Is Tarawih sunnah? 
Tarawih prayer is Sunnah mustahabbah (i.e., recommended) according to scholarly consensus, and comes under the heading of qiyam al-layl (night prayers). It is supported by the evidence of the Quran and Sunnah which encourages qiyam al-layl and describes its virtues. 
Reward for tarawih 
Praying qiyam in Ramadan is one of the greatest acts of worship by means of which a person can draw closer to his Lord in this month. Al-Hafiz Ibn Rajab said: “Note that in the month of Ramadan the believer engages in jihad al-nafs on two fronts: during the day by fasting and during the night by praying qiyam. Whoever combines these two types of jihad will be given reward without limit.”  
There are some hadiths which speak specifically about praying qiyam in Ramadan and describe the virtue of doing so. For example: 
Al-Bukhari (37) and Muslim (759) narrated from Abu Hurayrah that the Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever prays qiyam in Ramadan out of faith and in the hope of reward, his previous sins will be forgiven.” 
“Whoever prays qiyam in Ramadan” means spends its nights in prayer. 
“Out of faith” means, believing in Allah’s promise of reward. 
“And in the hope of reward” means, seeking the reward and with no other intention such as showing off etc. 
“Will be forgiven his previous sins”: 
Ibn al-Mundhir was certain that this includes both minor and major sins, but al-Nawawi said: What is known among the jurists is that this applies only to forgiveness of minor sins, not major sins. Some of them said: It may mean that the burden of major sins is reduced, so long as there are no minor sins.” (Fath al-Bari) 
Offering qiyam in the last ten days of Ramadan
The believer should be keen to strive in worship in the last ten nights of Ramadan more than at other times, because in these ten nights is Laylat al-Qadr , of which Allah says (interpretation of the meaning): 
“The Night of Al-Qadr (Decree) is better than a thousand months” [al-Qadr 97:3]
Reward for offering qiyam in Laylat al-Qadr
Concerning the reward of qiyam on this night, it is narrated that the Prophet (peace and blessings of Allah be upon him) said: “Whoever spends Laylat al-Qadr in prayer out of faith and in the hope of reward, his previous sins will be forgiven.” (Narrated by al-Bukhari, 1768; Muslim, 1268) 
Hence the Messenger of Allah (peace and blessings of Allah be upon him) used to strive hard in worship in the last ten nights as he did not do at other times. (Narrated by Muslim, 1175) 
Al-Bukhari (2024) and Muslim (1174) narrated that `Aishah (may Allah be pleased with her) said: “When the last ten days began, the Prophet (peace and blessings of Allah be upon him) would tie his lower garment (izar) tight and stay up at night, and wake his family.” 
“The last ten days” means the last ten days of Ramadan. 
“Tie his lower garment (izar) tight” - it was said that this is a metaphor for striving hard in worship, or for keeping away from his wives, and it may be that it includes both meanings. 
“stay up at night” means staying up and praying and doing other acts of worship. 
“And wake his family” means, he would wake them up to pray at night. 
Al-Nawawi said: 
“This hadIth indicates that it is mustahabb to do more acts of worship during the last ten nights of Ramadan, and to stay up at night to worship.” 
Offering Tarawih in congregation
We should be keen to pray qiyam al-layl in Ramadan in congregation , and to stay with the imam until he finishes praying. In this way, the worshipper will attain the reward for praying the whole night, even if he only spends a short part of the night in prayer. And Allah is the Owner of great bounty. 
Al-Nawawi (may Allah have mercy on him) said: 
The scholars agreed that it is mustahabb to pray Tarawih , but they differed as to whether it is better for a person to pray on his own at home or in congregation in the mosque. Al-Shafi`i and most of his companions, Abu Hanifah, Ahmad and some of the Malikis and others said that it is better to pray it in congregation, as `Umar ibn al-Khattab and the Companions (may Allah be pleased with them) did and as the Muslims continued to do. 
Al-Tirmidhi (806) narrated that Abu Dharr said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever prays qiyam with the imam until he finishes, will be recorded as having spent the whole night in prayer.” (Classed as sahih by al-Albani in Sahih al-Tirmidhi) 
And Allah knows best.