Kommasetzung vor bei?

If that’s a side set that starts with a preposition, definitely.

• The desk, on I’m just sitting, it’s not clean.
• You tell me, for which baker there are so delicious rolls?
• I don’t want to, with to spend Christmas with my mother-in-law.

But not otherwise:

• You go with me walk?
• What are you doing? with a longer traffic jam on the highway?
• Because of the continued rain the whole meadow under water.
• The whole meadow stands due to the continued rain under water.
• I’ll stay with strong cold to the house.