"I do not eat while leaning on my side."
He also said,
"I only sit like the slave sits and eat like the slave eats."
Leaning on the side harms the stomach because it prevents the food from going down the proper channel and reaching the stomach quickly,
as it pressures the stomach and does not allow it to be open properly for the food to pass through.
Eating while leaning on something is the practice of the arrogant people and this is why the Prophet (peace be upon him) said that,
"I only eat like the slaves eat."
The Prophet (peace be upon him) used to sit on his feet while eating. He used to place his knees on the ground and would place the bottom of his left foot on the upper part of his right foot in humility for the Lord and in respect for the food and for those present.
This is the best way for eating because the organs of the body will all be in their proper position, along with observing good manners.
As we have stated, the best to eat is sitting up with the organs of the body in their natural position.
The worst way of eating is leaning on one's side because the windpipe and the chewing organs will be pressured in this position and squeeze the stomach.
Also, the Prophet (peace be upon him) could have meant that he does not sit while leaning on pillows as the arrogant do and those who want to eat more food.
Rather, the Prophet (peace be upon him) used to eat what is barely sufficient just as the slave does.