How can one prove that the manas has stopped clinging?

When the manas does not engage in grasping, the mind is in meditative concentration (samādhi). As long as there is concentration, it indicates that the manas's grasping has weakened. At the second dhyāna and above, there is only the faint discrimination of the mind consciousness, indicating that the manas grasps even less. The reduction and cessation of the mind consciousness's functions both show that the manas no longer relies on the mind consciousness to discriminate mental sense-objects (dharma-viṣaya), and thus the manas has little grasping left. A concentration without the mind consciousness is the concentration of no perception (asaṃjñi-samāpatti); a concentration where the mental concomitants (caittas) of the mind consciousness's functions are reduced is the concentration of neither perception nor non-perception (naivasaṃjñānāsaṃjñā-samāpatti); and a concentration where the manas has reduced even its own functional mental concomitants is the cessation of perception and feeling (nirodha-samāpatti). When the manas completely and thoroughly ceases to grasp, one will enter Nirvāṇa without remainder (Anupadhiśeṣa-nirvāṇa).