Hadith: 'Abdullah Ibn 'Amr ibn 'As Radiyallahu 'anhuma narrates that Rasulullah Sallallahu 'alaihi wasallam said to me: O 'Abdullah! Do not be like so and so, who used to offer Tahajjud at night and then stopped offering it. (Bukhari: 1152)
Note: This hadith implies that without any valid excuse, the deeds in regular practice should not be given up. (Mazahir Haque)