lbn 'Abbaas Radiyallahu 'Anhu reports that:
"Rasulullah Sallallahu 'Alayhi Wasallam and his family spent many consecutive nights without food, because there would be no supper. The bread of Rasulullah Sallallahu 'Alayhi Wasallam was mostly made of barley". (Sometimes bread made of wheat was also available).
حَدَّثَنَا عَبْدُ اللهِ بْنُ مُعَاوِيَةَ الْجُمَحِيُّ، قَالَ‏:‏ حَدَّثَنَا ثَابِتُ بْنُ يَزِيدَ، عَنْ هِلاَلِ بْنِ خَبَّابٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ‏:‏ كَانَ رَسُولُ اللهِ صلى الله عليه وسلم، يَبِيتُ اللَّيَالِيَ الْمُتَتَابِعَةَ طَاوِيًا هُوَ وَأَهْلُهُ، لا يَجِدُونُ عِشَاءً وَكَانَ أَكْثَرُ خُبْزِهِمْ، خُبْزَ الشَّعِيرِ‏.‏
English reference : Book 24, Hadith 137
Arabic reference : Book 25, Hadith 145