Abu,Hurayra (Radhiallaahu Ánhu) relates that Rasulullah (Sallallaahu Álayhi Wasallam) said: “Many of those who fast obtain nothing through such fasting except hunger, and many a one performs “Salaat” by’ night but obtains nothing by it, except the discomfort of staying awake.”
With regard to this Hadith, the “Ulama” have mentioned three different interpretations: First, this Hadith may refer to those who fast during the day and then for “Iftaar” eat food that is “Haraam”; all the reward for fasting is lost because of the greater sin of eating ‘Haraam’ and nothing is gained except remaining hungry. Secondly, it may mean those who fast duly but, during fasting, engage themselves in backbiting and slandering others (see later). Thirdly, the person referred to may be one who, while fasting, did not stay away from evil and sin. In this Hadith all such possibilities are included. Similar is the case of the person performing ‘Salaat’ all night voluntarily; because of backbiting or any other sinful act (e.g. missing, Fajr salaat or keeping Awake for show), his night of devotion goes unrewarded.