SB 7.12.8

keśa-prasādhanonmarda-
snapanābhyañjanādikam
guru-strībhir yuvatibhiḥ
kārayen nātmano yuvā

keśa-prasādhana—brushing the hair; unmarda—massaging the body; snapana—bathing; abhyañjana-ādikam—massaging the body with oil and so on; guru-strībhiḥ—by the wife of the spiritual master; yuvatibhiḥ—very young; kārayet—should allow to do; na—never; ātmanaḥ—for personal service; yuvā—if the student is a young man.

If the wife of the spiritual master is young, a young brahmacārī should not allow her to care for his hair, massage his body with oil, or bathe him with affection like a mother.

The relationship between the student or disciple and the wife of the spiritual master or teacher is like that between son and mother. A mother sometimes cares for her son by combing his hair, massaging his body with oil, or bathing him. Similarly, the wife of the teacher is also a mother (guru-patnī), and therefore she may also care for the disciple in a motherly way. If the wife of the teacher is a young woman, however, a young brahmacārī should not allow such a mother to touch him. This is strictly prohibited. There are seven kinds of mothers:

ātma-mātā guroḥ patnī
brāhmaṇī rāja-patnikā
dhenur dhātrī tathā pṛthvī
saptaitā mātaraḥ smṛtāḥ

These mothers are the original mother, the wife of the teacher or spiritual master, the wife of a brāhmaṇa, the king's wife, the cow, the nurse and the earth. Unnecessary association with women, even with one's mother, sister or daughter, is strictly prohibited. This is human civilization. A civilization that allows men to mix unrestrictedly with women is an animal civilization. In Kali-yuga, people are extremely liberal, but mixing with women and talking with them as equals actually constitutes an uncivilized way of life.