Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (sallallaahu alayhi wa sallam) said,
“The best month for observing Saum (fasting) next after Ramadan is the month of Allah, the Muharram; and the best Salat (prayer) next after the prescribed Salat is Salat at night (Tahajjud prayers).”
Source: From Riyad-us-Saliheen (Chapter 225) : Dar-us-Salam English Publication
Narrated ‘Ubada bin As-Samit: The Prophet -sallAllaahu alayhi wa sallam-said:
“Whoever gets up at night and says: —
لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَه،ُ لَهُ الْمُلْكُ وَلَهُ الْحَمْد،ُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ
سُبْحَانَ اللَّهِ ، وَالْحَمْدُ لِلَّهِ ، وَلَا إِلَهَ إِلَّا اللَّهُ ، وَاللَّهُ أَكْبَرُ ،وَ لَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللَّهِ
‘There is none worthy of worship in truth except Allaah Alone, He has no partners, He has the Dominion and for Him is all praise, and He is capable of all things, praise is for Him, and Far is Allaah from imperfection, and There is none worthy of worship in truth except Allaah, and Allaah is the Greatest, there is no capability nor is there any power except with Allaah.
La ilaha ‘illa Allaahu wahdahu la shareeka lahu, lahul mulku wa lahul hamdu wa huwa ala kulli shayin qadeer Subhana allaahi, wal hamdu lillaahi, wa la illaah ila Allaah, wa Allaahu akbar, La hawla wa la quwwata illa billaa
Then he says : اللهمَ اغْفِرْلي O Allaah forgive me (Allaahumma aghfirlee), or he supplicates and his supplication is answered, and if he makes Wudu and prays then his prayer is accepted.
Sahih Bukhari Volume 2, Book 21, Number 253 : Prayer at Night (Tahajjud
Translated by Muhsin Khan