Aśauca-vidhi (Rules of Impurity) within Śrāddha-kalpa — Chapter on Testing/Selecting Brahmanas and Honoring the Atithi
सांगुष्ठेन तथा पाद्यं नासुरेभ्यो यथा भवेत् / एतान्येव च सर्वाणि दानानि च विशेषतः
sāṃguṣṭhena tathā pādyaṃ nāsurebhyo yathā bhavet / etānyeva ca sarvāṇi dānāni ca viśeṣataḥ
The pādya should be offered in the manner that includes the thumb, so that it does not go to the Asuras; and especially these alone are the prescribed gifts (in the śrāddha).