Maimuna said that when the Prophet prostrated himself he kept his arms so far away from his sides that if a lamb had wanted to pass under his arms it could have done so. This is Abu Dawud’s wording, as [Baghawi] explained in Sharh as-sunna with his isnad. Muslim has something to the same effect:She said that when the Prophet prostrated himself, if a lamb had wanted to pass between his arms it could have done so.
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 890
Hadith Gradingالألبانی:صَحِيح | زبیر علی زئی:صحيح
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «صحيح، رواه أبو داود (898) و البغوي في شرح السنة (3/ 145، 146) و مسلم (237/ 496)»