The Prophet Muhammad ﷺ slept on his right side. Al-Bara' ibn 'Azib reported: "When the Prophet ﷺ wanted to sleep, he would lie down on his right side." (Narrated by Al-Bukhari, no. 6315, and Muslim, no. 2710).
This prophetic recommendation to sleep on the right side must be examined in light of modern medicine with caution and nuance, because scientific research does not provide a simple consensus on the ideal sleeping position for healthy people.
Several clinical studies have shown benefits of the lateral position in specific contexts. In patients with congestive heart failure, the right lateral position has been associated with reduced dyspnea (breathing difficulty) compared with the left lateral position. The lateral position in general helps keep the airways open and may reduce sleep apnea in some patients.
However, the literature on gastroesophageal reflux disease (GERD) recommends sleeping on the left side, which reduces acid reflux. For healthy people, there is no scientific consensus establishing that one lateral position is superior to the other.
Caution is therefore required: the convergence between the prophetic recommendation and science is partial and contextual. The documented benefits of the right lateral position mainly concern specific clinical contexts (congestive heart failure), not a general superiority for all sleepers. This convergence is therefore fragile and must be presented with nuance.