Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever wakes up at night and says: 'La ilaha illallahu wahdahu la sharika lah, lahul-mulku wa lahul-hamd, wa huwa 'ala kulli shay'in qadir, subhanallah, walhamdu lillah, wa la ilaha illallah, wallahu akbar, wa la hawla wa la quwwata illa billah' (There is no god but Allah, alone, without partner; His is the dominion and His is all praise, and He has power over all things. Glory be to Allah, all praise is for Allah, there is no god but Allah, Allah is the Greatest, and there is no power to turn away from evil and no strength to do good except by Allah's enabling), and then says: 'Rabbighfir li' (My Lord! Forgive me), he is forgiven." Or he said: "Then he supplicates and his supplication is answered; and if he resolves, gets up, performs ablution and prays, his prayer is accepted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4667