بُلُوغُ الْمَرَامِ
Bulugh al-Maram 444
The Book of Prayer
وَعَنْ عَائِشَةَ رَضِيَ اَللَّهُ عَنْهَا قَالَتْ: { رَأَيْتُ اَلنَّبِيَّ - صلى الله عليه وسلم -يُصَلِّي مُتَرَبِّعًا } رَوَاهُ النَّسَائِيُّ. وَصَحَّحَهُ اَلْحَاكِمُ.
Narrated 'Aishah (RA): I saw the Prophet (ﷺ) praying while sitted in a cross-legged position. [Reported by an-Nasa'i; and al-Hakim graded it Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 359