Śatapatha Brāhmaṇa ("of a hundred paths") 11.5.4.14

11.5.4.14

atha haike dakṣiṇataḥ tiṣṭhate vāsīnāya vānvāhurna tathā kuryādyo hainaṃ tatra brūyādbulbaṃ nvā ayamimamajījanata bulbo bhaviṣyatītīśvaro ha tathaiva syāttasmātpurastādeva pratīce samīkṣamāṇāyānubrūyāt

And some recite it to him while he (the student) is standing or sitting on (the teacher's) right side; but let him not do this; for if, in that case, any one were to say of him, 'Surely, this (teacher) has born this (student) sideways, he will become averse to him;' then that would indeed be likely to come to pass: let him therefore recite it in a forward (easterly) direction to (the student) looking at him towards the west.