Aśauca-vidhi (Rules of Impurity) within Śrāddha-kalpa — Chapter on Testing/Selecting Brahmanas and Honoring the Atithi
अभ्यागतः पाकचारदतिथिः स्यादपावकः / अतिथेरतिथिः प्रोक्तः सो ऽतिथिर्योग उच्यते
abhyāgataḥ pākacāradatithiḥ syādapāvakaḥ / atitheratithiḥ proktaḥ so 'tithiryoga ucyate
A guest who arrives at the time of the meal is called ‘apāvaka’; and the guest of a guest is declared to be the atithi known as ‘yoga’.