Shama-il Tirmidhi Chapter 027, Hadith Number 004 (182).
Abu Sa'eed Khudari Radiyallahu 'Anhu says: "After eating Rasulullah Sallallahu 'Alayhi Wasallam read this du'aa:
Alhamdulillaahil-ladhi at-amanaa wa-saqaa-naa wa-ja-a-lanaa muslimeen.
Praise be to Allah who fed us, and gave us drink and made us muslims".
It is evident that after eating we must thank Allah and as stated in the Qur-aan: '...if you give thanks to Me I will increase for you'. - Surah Ebrahim, 7.
This an opportunity for giving-thanks. The word 'made us Muslims' is included because together with worldly favours, Allah has granted us spiritual favours by making us Muslims. Or because in reality the offering of thanks for eating and drinking and also the praising and thanking of Allah is the result of Islaam. Therefore this too has been included.