Pārāyanavagga

Suttapiṭaka · Khuddakanikāya · Cūḷaniddesa · Vol. 30 · Section 47

[47] He covers his face with his tongue; a tuft of hair (uṇṇā) lies between his eyebrows; his male organ, concealed by clothing, is enclosed in a sheath — know it thus, young man (māṇava).

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.