Shama-il Tirmidhi Chapter 027, Hadith Number 003 (181).
Umar bin Abi Salamah Radiyallahu 'Anbu came to Rasululah Sallallahu 'Alayhi Wasallam while food had been served to him. Rasulullah Saliallahu 'Alayhi Wasallam said: "O my Son come near, recite Bismillah, and eat with your right hand from that portion which is in front of you".
The 'ulama are unanimous that it is sunnah to recite 'Bismillah'. According to the majority it is sunnah to eat with the right hand, and some say it is waajib. The reason being Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam cursed a person who ate with his left hand, subsequently that persons hand became paralysed. This exemplary incident is mentioned in the kitaabs of hadith,that a person was eating with the left hand. Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam advised him to eat with the right hand. He replied: 'I cannot eat with the right hand'. Sayyidina Rasulullah Saliallahu 'Alayhi Wasallam said: 'You will not be able to eat with it in the future also'. After that, his right hand did not reach his mouth. In another narration it is related that Sayyidina RasulIullah Sallallahu 'Alayhi Wasallam once saw a woman eating with her left hand. 'Sayidina Rasulullah Sallallahu 'Alayhi Wasallam cursed her, the woman died in a plague. It is stated in Ibn Maajah that Sayyidina Rasulullah Sallailahu 'Alayhi Wasallam said: 'The shaytaan eats with the left hand, therefore do not eat with the left hand'. According to some 'ulama, because of this narration, it is waajib to eat with the right hand. The majority of the 'ulama say it is sunnaah. Nevertheless, due to these ahaadith strict importance should be paid to eating with the right hand. Nowadays people do not pay head to this, especially when drinking water (and tea). This disease has spread wildly. Sayyidina Rasulullah Sallallahu 'Alayhi Wasallam has commanded, 'Eat with the right hand and drink with the right hand because the shaytaan eats and drinks with the left hand'. In the same manner according to some 'ulama it is waajib to eat from one's ownside (the food that is before one), but according to the majority it is sunnah.