When it comes to our day to day activities, we are careless about some things that are given some importance in the light of Islam. For example, stepping into the house with the right foot first and various other small, yet significant activities are considered important in the light of Islam.
When it comes to sleeping, Muslims are aware of the fact that they should sleep on the right side and should perform wazzu before sleeping and that they should recite the dua before going to bed. However, not many focus on the sleeping position that Allah does not like.
On one occasion, the Prophet Muhammad SAWW saw a man lying on the ground on his stomach. The Prophet SAWW went up to him, woke him up by nudging the man with his foot. The man woke up and looked at the Prophet SAWW’s face. The Prophet SAWW then told him, “this is the method of lying which God hates. This is how people in hell lie.” (Reported by Ahmad, al-Fath al-Rabbaani, 14/244-245; by al-Tirmidhi, no. 2798, Shaakir edn.; and by Abu Dawood, al-Sunan, Kitaab al-Adab, no. 5040, al-Da’aas edn. Also reported in Saheeh al-Jaami’, 2270-2271)
Ya’eesh ibn Tihfah al-Ghifaari reported that his father said: “I stayed as a guest with the Messenger of Allaah (peace and blessings of Allaah be upon him) with those of the poor whom he hosted. The Messenger of Allah (peace and blessings of Allaah be upon him) came out in the night to check up on his guests and saw me lying on my stomach. He prodded me with his foot and said, ‘Do not lie in this manner, for it is a way of lying that Allaah hates.’”
This goes for both genders and scientifically, it is also not advised due to digestion concerns that arise due to sleeping on stomach on regular basis.