The reviver of Sunna Shaikh Mawlana Abrarul Haqq (Allah have mercy on him) said,

‘The tahajjud salah in itself has the property to make an individual righteous, pious and a friend (wali) of Allah.’

‘There are some medicines that have the property of working both at preventing the disease (prophylaxis) and eradicating it (treatment). Similar is the case of tahajjud. It  eradicates the sinful deeds and nurtures the resistance for indulgence in sinful.’

Ma’arif al Abrar ra, page 238