We had a session recently wherein a character went down in combat due to a creature attack. Two other characters stepped up to engage the creature while a third attempted to stabilize the downed character and thus help/circumvent the character having to make his death saving throws. Our DM stated that the character attempting to stabilize would have an attack of opportunity from the creature. (The character providing aid did not move out of the reach of the opponent.)
As I remember from the rules as written, in 5e attacks of opportunity are only generated when a character moves out of a creatures threat range. Was my DM right?