Shama-il Tirmidhi Chapter 027, Hadith Number 001 (179).
Abu Ayyub Ansaari Radiyallahu'Anhu reports: "We were once present in the assembly of Rasulullah Sallallahu 'Alayhi Wasallam. Food was brought to him. 1 did not observe any food that had so much barakah at the beginning and at the end of which there was no barakah left in the food. We therefore asked Rasulullah Sallallahu 'Alayhi Wasallam reason?. He replied: 'In the beginning we all recited 'Bismillah' before we began eating. Then someone in the end joined us, and did not recite ''Bismillah'. The shayiaan ate with him'".
According to the majority of the 'ulama, by the word 'Sh'aytaan eating the actual meaning is intended. It is not impossible for the shaytaan to eat and drink. In this hadith only Bismillah is mentioned, therefore the 'ulama say, if one only recites Bisrnillah before eating, it will suffice, but it is better and recommended that the full 'Bismillahir Rahmanir Rahim' be recited. The 'ularna have also written that it is better to say the bismillah audibly so that others who may have forgotten may also remember it.