i remember hearing this from shaykh al-yaqu`bi. inshAllah, when i find the audio, i can post it. wassalam
this is attributed to sayyiduna 'ali radiyallahu anh. there were 2 men, one had 3 rotis and the other had 5. another man joined them who had no rotis. they invited him to eat with them. they couldnt divide 8 rotis between 3 so they just had a third each of each roti (8*3 = 24 pieces) cant remember properly but they then went to our master 'ali radiyallahu anh and said how many rotis are we owed? sayyiduna 'ali said the man who had 3 rotis is owed one and the man who had 5 is owed 7. they asked how? 'Ali said the man who had 3 rotis had 9 pieces (3 pieces per roti) and ate 8 and the man who had 5 rotis had 15 pieces and also ate 8. so he is owed 7 pieces and the 3 roti man is owed 1. i havent told it too well cos i cant remember the story but told properly it is amazing.