Narrated `Aisha:

Whenever the Prophet () took the bath of Janaba (sexual relation or wet dream) he asked for the Hilab or some other scent. He used to take it in his hand, rub it first over the right side of his head and then over the left and then rub the middle of his head with both hands.

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا أَبُو عَاصِمٍ، عَنْ حَنْظَلَةَ، عَنِ الْقَاسِمِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا اغْتَسَلَ مِنَ الْجَنَابَةِ دَعَا بِشَىْءٍ نَحْوَ الْحِلاَبِ، فَأَخَذَ بِكَفِّهِ، فَبَدَأَ بِشِقِّ رَأْسِهِ الأَيْمَنِ ثُمَّ الأَيْسَرِ، فَقَالَ بِهِمَا عَلَى رَأْسِهِ‏.‏

Reference	: Sahih al-Bukhari 258
In-book reference	: Book 5, Hadith 11