SB 7.15.36
yah pravrajya grhat purvam
tri-vargavapanat punah
yadi seveta tan bhiksuh
sa vai vantasy apatrapah
Translation:
One who accepts the sannyasa order gives up the three principles of materialistic activities in which one indulges in the field of household life — namely religion, economic development and sense gratification. One who first accepts sannyasa but then returns to such materialistic activities is to be called a vantasi, or one who eats his own vomit. He is indeed a shameless person.
Purport:
Materialistic activities are regulated by the institution of varnasrama-dharma. Without varnasrama-dharma, materialistic activities constitute animal life. Yet even in human life, while observing the principles of varna and asrama — brahmana, ksatriya, vaisya, sudra, brahmacarya, grhastha, vanaprastha and sannyasa — one must ultimately accept sannyasa, the renounced order, for only by the renounced order can one be situated in brahma-sukha, or transcendental bliss. In brahma-sukha one is no longer attracted by lusty desires. Indeed, when one is no longer disturbed, especially by lusty desires for sexual indulgence, he is fit to become a sannyasi. Otherwise, one should not accept the sannyasa order. If one accepts sannyasa at an immature stage, there is every possibility of his being attracted by women and lusty desires and thus again becoming a so-called grhastha or a victim of women. Such a person is most shameless, and he is called vantasi, or one who eats that which he has already vomited. He certainly leads a condemned life. In our Krsna consciousness movement it is advised, therefore, that the sannyasis and brahmacaris keep strictly aloof from the association of women so that there will be no chance of their falling down again as victims of lusty desires.