مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 346
Purification
How to act when relieving oneself - Section 2
وَعَنْ أَنَسٍ رَضِيَ اللَّهُ عَنْهُ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا أَرَادَ الْحَاجَةَ لَمْ يَرْفَعْ ثَوْبَهُ حَتَّى يَدْنُوَ مِنَ الأَرْض. رَوَاهُ التِّرْمِذِيّ وَأَبُو دَاوُد والدارمي
Anas said that when the Prophet (ﷺ) wanted to relieve himself he did not raise his garment till he was near the ground. Tirmidhi, Abu Dawud and Darimi transmitted it.
Mishkat al-Masabih, 346صَحِيحٌ (الألباني)