Muwatta Malik 101

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَائِشَةَ، سُئِلَتْ عَنْ غُسْلِ الْمَرْأَةِ، مِنَ الْجَنَابَةِ فَقَالَتْ لِتَحْفِنْ عَلَى رَأْسِهَا ثَلاَثَ حَفَنَاتٍ مِنَ الْمَاءِ وَلْتَضْغَثْ رَأْسَهَا بِيَدَيْهَا ‏.‏

Yahya related to me from Malik that he had heard that A'isha was asked about how a woman should do ghusl for major ritual impurity. She said, "She should scoop water over her head with both hands three times and rub the roots of her hair with her hands

Reference

Muwatta Malik 101

In-book

Book 2, Hadith 70