It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that he said: It is written in the Torah that Allah Almighty has prepared, for those whose sides forsake their beds (that is, those who pray tahajjud), that which no eye has seen, no ear has heard, and which has never occurred to the heart of any human being, and which no angel brought near knows nor any prophet sent as a messenger. He said: And we read it (in the Qur'an) thus: [Surah al-Sajdah: 17] "So no soul knows what has been kept hidden for them of the comfort of the eyes, as a reward for what they used to do." This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.