مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 543
Purification
Washing as Established by the Sunna - Section 2
وَعَن قيس بن عَاصِم: أَنَّهُ أَسْلَمَ فَأَمَرَهُ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنْ يَغْتَسِلَ بِمَاءٍ وَسِدْرٍ. رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالنَّسَائِيُّ
Qais b. ‘Asim said that when he accepted Islam the Prophet (ﷺ) commanded him to bathe with water and lote-tree leaves. Tirmidhi, Abu Dawud and Nasa’i transmitted it.
Mishkat al-Masabih, 543صَحِيح (الألباني)