Riyad as-Salihin, Book 5, Hadith 823 (In-Book)

Qailah bint Makhramah (May Allah be pleased with her) reported: I saw the Prophet seated with his arms enfolding his legs; and when I saw him in such a state of humble guise I trembled with fear due to the awe (he showed in that posture).[At-Tirmidhi].

وعن قيلة بنت مخرمة رضى الله عنها قالت‏:‏ رأيت النبي صلى الله عليه وسلم وهو قاعد القرفصاء، فلما رأيت رسول الله صلى الله عليه وسلم المتخشع في الجلسة أرعدت من الفرق‏.‏ ‏‏ ‏.‏

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