Sahih al-Bukhari 167
Sahih al-Bukhari · Book 4: Ablutions (Wudu') · While performing ablution or taking a bath one should start from the right side of the body
Narrated Um-`Atiya:
حَدَّثَنَا مُسَدَّدٌ ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ ، قَالَ حَدَّثَنَا خَالِدٌ ، عَنْ حَفْصَةَ بِنْتِ سِيرِينَ ، عَنْ أُمِّ عَطِيَّةَ ، قَالَتْ قَالَ النَّبِيُّ صلى الله عليه وسلم لَهُنَّ فِي غُسْلِ ابْنَتِهِ " ابْدَأْنَ بِمَيَامِنِهَا وَمَوَاضِعِ الْوُضُوءِ مِنْهَا " .
That the Prophet (ﷺ) at the time of washing his deceased daughter had said to them, "Start from the right side beginning with those parts which are washed in ablution."