What is the meaning of the phrase "one of the conditions for acting upon a weak hadith is that it falls under an established principle acted upon," along with a request for clarification and examples?

Acting upon a weak Hadith concerning the virtues of deeds stipulates that it must fall under an established principle that is already acted upon. This means that the act or omission mentioned in the weak Hadith must have its ruling already indicated by another evidence. The weak Hadith then comes to mention a specific reward or punishment for performing or abandoning that act. The exact amounts of reward and punishment, whether they are established or not, do no harm, provided the Hadith is not fabricated. An example of this is the Hadith about entering the marketplace: remembrance (dhikr) in the marketplace is generally recommended, and the reported estimation of its reward, whether it is established or not, does no harm. Imam Ibn Daqeeq al-Eid explicitly stated that what is meant by acting upon a weak Hadith is to include it under general rulings regarding the action itself, not to establish its specific form as recommended solely by that Hadith.