"Verily between man and between polytheism and unbelief is the negligence of prayer." (Muslim)
It is narrated on the authority of 'Abdullah b. Mas'ud(Radi Allah Anhu) that he observed. I asked the Messenger of Allah (sal-allahu- alleihi-wasallam ) which deed was the best. He (the Holy Prophet) replied: Prayer at its appointed hour. I (again) said: Then what? He (the Holy Prophet) replied: Kindness to the parents. I (again) said: Then what? He replied: Earnest endeavour (Jihad) in the cause of Allah. And I would have not ceased asking more questions but out of regard (for his feelings). (Muslim)
Narrated Uthman ibn Affan (RAA) Rasulullah (SAW) at the time of our returning from our prayer told us (certain things pertaining to purification).
He said: I do not know whether I should tell you a thing or keep quiet. We said: Rasulullah, tell us if it is good and if it is otherwise, Allah and Messenger (SAW) know better. Upon this he said: A Muslim who purifies (himself) and completes purification as enjoined upon him by Allah and then offers the prayers, that will be expiatious (of his sins he committed) between these (prayers). (Sahih Muslim Book 2, Hadith # 0444)
Narrated Jabir ibn Abdullah (RAA) Rasulullah (SAW) said: The similitude of five prayers is like an overflowing river passing by the gate of one of you in which he washes five times daily. Hasan said: No filthiness can remain on him. (Sahih Muslim Book 4, Hadith # 1411)
Narrated Abu Hurairah (RAA) Rasualullah (SAW) said, "No prayer is harder for the hypocrites than the Fajr and the 'Isha' prayers and if they knew the reward for these prayers at their respective times, they would certainly present themselves (in the mosques) even if they had to crawl." The Prophet added, "Certainly I wish to order the Mu'adh-dhin (call-maker) to pronounce Iqama and order a man to lead the prayer and then take a fire flame to burn all those who had not left their houses so far for the prayer along with their houses." (Sahih Al-Bukhari Volume 1, Book 11, Hadith # 626)