Abbad bin Tamim reported,

His uncle reported that he saw the Messenger of Allah ﷺ lying on his back in the mosque, with one leg resting over the other.Saeed bin Musayab said, "Umar and Uthman used to do the same."

Azami 14735

Sahih

عن عباد بن تميم

عن عمه، أنه رأى رسول الله ﷺ مستلقيا في المسجد، واضعا إحدى رجليه على الأخرى. قال سعيد بن المسيب: كان عمر وعثمان يفعلان ذلك.

الأعظمي 14735صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Superior moral conduct
Chapter
Etiquette of night and day
Section
Permissibility of lying on one's back if the private parts are not exposed
Numbering
Jami al-Kamil 14735 (2nd edition)
Azami 14735