Madhvaon Brahma Sūtra 3.3.45

It is not obligatory that he who is at first sought as preceptor is to be the only preceptor ; even another pre- ceptor that may happen to be afterwards found, may also be betaken to, if the latter is capable of conferring on him (the pupil) the full grace (i.e. the full light of knowledge for which he is eligible). If the latter should happen to be an equal, superior, or inferior, to the first preceptor, and if he should of his own accord offer his instruction then, i.e., either in accepting him or rejecting him, an option has to be exercised, as in the case of mental acts (i.e., in two acts of meditation of equal efficacy, (either of them may be chosen). The following is in the Brihat Tantra: “If a preceptor superior to the first should of his own accord come to the pupil, he may be accepted without a question; but it is optional in the Case of equals. Not having received the full grace, Satyakama with the permission of Rishabha and others went back to his preceptor and from him obtained it (the perfect grace), which is of course just.” Also in the Maha Samhita : “ If another preceptor equal to the first should of himself (offer to) show perfect grace, (then) the pupil may, with the permission of the first, unquestionably accept him. Just as there is a choice between two acts of meditation tending to the same purpose, so also it is in the matter of going to a second preceptor.”