ENOfficial
Anas said that God's messenger used to have himself cupped in the two veins at the sides of the neck and on the shoulder. Abu Dawud transmitted it, and Tirmidhi and Ibn Majah added that he used to have himself cupped on the 17th, 19th, and 21st.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَنَسٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَحْتَجِمُ فِي الْأَخْدَعَيْنِ وَالْكَاهِلِ. رَوَاهُ أَبُو دَاوُدَ وَزَادَ التِّرْمِذِيُّ وَابْنُ مَاجَهْ: وَكَانَ يحتجمُ سبعَ عشرَة وتسع عشرَة وَإِحْدَى وَعشْرين
sunnah.com