What is the recommended spacing between the feet while standing?
Chapter on what invalidates the prayer if omitted intentionally or forgetfully
Al-Mughni
Book of Prayer
Primary text
It is recommended that the worshipper separate their feet slightly. Evidence for this is found in the narration where Abdullah saw a man praying with his feet held tightly together and commented that it would have been better had he shifted his weight between them. This action of shifting weight is supported by the practice of Abu Abdullah (Ahmad ibn Hanbal) and is narrated from Amr ibn Maymun and Al-Hasan.
Supporting text
If the standing period is prolonged, shifting weight between the feet is permissible or even recommended, as indicated by 'Ata, suggesting that frequent movement should generally be minimized in voluntary prayers unless the length of the standing necessitates resting weight alternatively on one foot then the other.