KAṬHA UPANISHAD · 1.1.9

तिस्रो रात्रीर्यदवात्सीर्गृहे मेऽनश्नन् ब्रह्मन्नतिथिर्नमस्यः ।
नमस्तेऽस्तु ब्रह्मन् स्वस्ति मेऽस्तु
तस्मात्प्रति त्रीन्वरान्वृणीष्व ॥ ९॥

tisro rātrīryadavātsīrgṛhe me’naśnan brahmannatithirnamasyaḥ ।
namaste’stu brahman svasti me’stu
tasmātprati trīnvarānvṛṇīṣva ॥ 9॥

“Because for three nights thou hast dwelt in my house, O Brahmin, a guest worthy of reverence, — salutation to thee, O Brahmin, on me let there be the weal, — therefore three boons do thou choose; for each night a boon.”

Sri Aurobindo · CWSA 18, p. 102