Śaṅkaraon Brahma Sūtra 3.3.61

Are those — meditations enjoined in the three Vedas which rest on members of sacrificial actions such as the udgitha to be superadded to each other, or may we proceed with regard to them as we like?—To this doubt the Sintra replies, ‘ it is according to the abodes/ As the abiding- places of those meditations, viz. the Stotra and so on, are combined (for the performance of the sacrifice), so those meditations also. For a meditation is subject to what it rests on.