Exodus 13:21 - 22
ESV - 21 And the Lord went before them by day in a pillar of cloud to lead them along the way, and by night in a pillar of fire to give them light, that they might travel by day and by night. 22 The pillar of cloud by day and the pillar of fire by night did not depart from before the people.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.