Thrice
Srimad-Bhagavatam
SB Canto 1
SB 1.14.43, Purport:
It is the duty of a householder to feed first of all the children, the old members of the family, the brāhmaṇas and the invalids. Besides that, an ideal householder is required to call for any unknown hungry man to come and dine before he himself goes to take his meals. He is required to call for such a hungry man thrice on the road. The neglect of this prescribed duty of a householder, especially in the matter of the old men and children, is unpardonable.