It was the practice of the Prophet (peace and blessings be upon him):
"His (peace and blessings be upon him) hair was shorter than a jummah (hair reaching the shoulders) and longer than a wafrah (hair reaching the earlobes)."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4817
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[ت في الشمائل٢ هـ] عن عائشة. المشكاة ٤٤٦٠.