The reason of not lighting fires is, because there was nothing to cook. The 'ulama have written that water is mentioned because there were not enough dates, and without water the stomach could not be filled. First a few dates were eaten, thereafter an amount of water was drunk to fill the stomach. In another hadith it is stated 'Two full months would pass and the hilaal for the third month would be observed, and no circumstances warranted that a fire be lit in the houses of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam for cooking'. In a hadith it is stated: 'One month passed, then another month passed, there was no such occasion where a fire was lit in any of the houses of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam'. 'Urwah Radiyallahu 'Anhu asked his aunt Sayyiditina 'Aayeshah Radiyallahu 'Anha, 'O Aunt, on what did you sustain yourself? She replied: 'Dates and water. There were a few neighbours of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam from among the Ansaar who owned some animals that gave milk. If one of them sent some milk as a present, then we too would partake of it'. In a hadith it is stated: 'Once for one and half months continuously, no fire was lit in the house of Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam for illumination or other purposes'. Fire for illumination means that a lamp or candle did not burn. Jam'ul Wasaa'il.
 

In a hadith it is narrated that Sayyidina Abubakr Radiyallahu 'Anbu once presented a leg of a goat. It was night time and Sayyiditina 'Aayeshah Radiyallahu 'Anha began cutting it into pieces in the dark. Someone said.. 'There is no lamp in the house'. She began to say: 'If there was oil for a lamp, would it not have been used for cooking?' The 'ulama have written that Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam preferred this way for himself and his family, although the keys of treasures were presented to him. The ummah thereafter split into four groups. One is that group that did not take interest in the material aspects of the world, nor did the world go towards them, like Sayyidina Abubakr Siddiqe Radiyallahu 'Anhu. The second group are those who did not take interest in worldly things, but the world took interest in them, like Sayyidina 'Umar Faaruq Radiyallahu 'Anhu. The third group are those who took interest in the material world, and the world also took interest in them, like the Banu Umayyah kings excluding 'Umar bin 'Abdul 'aziz Radiyallahu 'Anhu. The fourth group are those who went seeking for the material world, but the world did not turn towards them, like the one's whom Allah Ta'aala has made poor, and the love for the world has settled in their hearts. - Munaawi.