Muwatta Malik, Book 50, Hadith 1728 (In-Book) ⓘ

Yahya related to me from Malik from Hisham ibn Urwa from Fatima bint al-Mundhir that whenever a woman who had a fever, was brought to Asma bint Abi Bakr, she made dua for her and took water and poured it inside her collar. She said, "The Messenger of Allah, may Allah bless him and grant him peace, ordered us to cool it with water."

حَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ فَاطِمَةَ بِنْتِ الْمُنْذِرِ، أَنَّ أَسْمَاءَ بِنْتَ أَبِي بَكْرٍ، كَانَتْ إِذَا أُتِيَتْ بِالْمَرْأَةِ وَقَدْ حُمَّتْ تَدْعُو لَهَا أَخَذَتِ الْمَاءَ فَصَبَّتْهُ بَيْنَهَا وَبَيْنَ جَيْبِهَا وَقَالَتْ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَأْمُرُنَا أَنْ نُبْرِدَهَا بِالْمَاءِ ‏.‏