ENOfficial
It was narrated that Anas bin Malik said: "When Khamr was forbidden, their drink was (made from) unripe dates and dried dates."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ حُمَيْدٍ الطَّوِيلِ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ حُرِّمَتِ الْخَمْرُ حِينَ حُرِّمَتْ وَإِنَّهُ لَشَرَابُهُمُ الْبُسْرُ وَالتَّمْرُ.
sunnah.com