مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 359
Purification
How to act when relieving oneself - Section 2
وَعَنْ عَائِشَةَ قَالَتْ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا خَرَجَ مِنَ الْخَلَاءِ قَالَ «غفرانك» . رَوَاهُ التِّرْمِذِيّ وَابْن مَاجَه والدارمي
‘A'isha told that when the Prophet (ﷺ) came out from the privy he said, "Grant Your forgiveness.” Tirmidhi, Ibn Majah and Darimi transmitted it.
Mishkat al-Masabih, 359صَحِيح (الألباني)