Manusmriti

siva.sh/manusmriti/3/102

एकरात्रं तु निवसन्नतिथिर्ब्राह्मणः स्मृतः । अनित्यं हि स्थितो यस्मात् तस्मादतिथिरुच्यते ॥ १०२ ॥

sanskrit

But a Brahmana who stays one night only is declared to be a guest (atithi); for because he stays (sthita) not long (anityam), he is called atithi (a guest).

english translation

ekarAtraM tu nivasannatithirbrAhmaNaH smRtaH | anityaM hi sthito yasmAt tasmAdatithirucyate || 102 ||

hk transliteration by Sanscript