Musnad Ahmad 30:737

Ayyub ibn al-Najjar Abu Isma'il al-Yamami narrated to us, from Tayyib ibn Muhammad, from 'Ata' ibn Abi Rabah, from Abu Hurayrah, who said: "The Messenger of Allah, may Allah bless him and grant him peace, cursed the effeminate men who imitate women, and the masculine women who imitate men, and the one who travels through the wilderness alone."