Narrated Abu Huraira:Allah’s Apostle said, “When it is the last third of the night, our Lord, the Blessed, the Superior, descends every night to the heaven of the world and says, ‘Is there anyone who invokes Me (demand anything from Me), that I may respond to his invocation; Is there anyone who asks Me for something that I may give (it to) him; Is there anyone who asks My forgiveness that I may forgive him?’ “
Bukhari, Volume 8, Book 75, Number 333
This is why praying Tahajjud has such a big significance at that hour of the night.
Allah S.W.T. gives us the chance to ask for forgiveness and seek his blessings every night, we should try to make the most of it and not let go of such opportunities for few minutes of sleep.