Musnad Ahmad 31:206

Yunus ibn Muhammad narrated to us, Hammad ibn Salamah narrated to us, from Sa'id al-Jurayri, from Abu Nadrah, from Abu Sa'id al-Khudri, that the Messenger of Allah (may Allah bless him and grant him peace) asked Ibn Sayyad about the soil of Paradise. He said: "White musk flour." He said: So the Messenger of Allah (may Allah bless him and grant him peace) said: "He has spoken the truth."