That's a toughie. On the one hand, all other things being equal, you're not hiring anyone from that religion because of their religious observances.
On the other hand, you need someone who'll work more than 3 days / week. If they don't wish to work more than 3 days, you'll find someone who will. Your discrimination is incidental.
All in all, I'd say yes. But at the same time, I wouldn't necessarily judge you harshly for it. There aren't any travelling sales reps who are single mothers, but no one is blasting the sales rep's companies over it.