Some ahadith

Narrated AbuUmamah:

The Prophet (peace_be_upon_him) said: I guarantee a house in the surroundings of Paradise for a man who avoids quarreling even if he were in the right, a house in the middle of Paradise for a man who avoids lying even if he were joking, and a house in the upper part of Paradise for a man who made his character good. (Abu Dawud :: Book 41 : Hadith 4782)

Umm Habiba, the wife of the Apostle of Allah (may peace be upon him), reported Allah's Messenger (may peace be upon him) as saying: If any Muslim servant (of Allah) prays for the sake of Allah twelve rak'ahs (of Sun'an) every day, over and above the obligatory ones, Allah will build for him a house in Paradise, or a house will be built for him in Paradise; and I have not abandoned to observe them after (hearing it from the Messenger of Allah). (So said also 'Amr and Nu'man.) (Muslim :: Book 4 : Hadith 1581)

Narrated Ubayy ibn Ka'b:

The Apostle of Allah (peace_be_upon_him) led us in the dawn prayer one day. And he said: Is so and so present? They said: No. He (again) asked: Is so and so present? They replied: No. He then said: These two prayers are the ones which are most burdensome to hypocrites. If you knew what they contain (i.e. blessings), you would come to them, even though you had to crawl on your knees. The first row is like that of the angels, and if you knew the nature of its excellence, you would race to join it.

A man's prayer said along with another is purer than his prayer said alone, and his prayer with two men is purer than his prayer with one, but if there are more it is more pleasing to Allah, the Almighty, the Majestic.