Praise be to Allaah.
The reason for this is that it was forbidden by the Prophet (peace and blessings of Allaah be upon him), who left no good thing but he told us about it and left no evil thing but he warned us against it. 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 Allaah (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.’” According to another report, the Prophet (peace and blessings of Allaah be upon him) prodded him with his foot and woke him up, and said, “Do not lie like this, for this is how the people of 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)
This is a general prohibition that applies to both males and females, because the basic principle is that rulings apply to both sexes, except in cases where it is indicated that there is a differentiation between the two. And Allaah knows best.