The correct passive form of the given sentence is:

☀ It must never be said that he was ungenerous.

Let's break down the options:

1. It must never be said that he was ungenerous. (Correct) This sentence correctly uses the passive voice and conveys the same meaning as the original sentence. It uses the correct form "must never be said."

2. He was ungenerous is not said by you. (Incorrect) This option changes the meaning of the original sentence. It suggests that the subject "you" is not saying that "he was ungenerous," rather than expressing prohibition as in the original sentence. The correct form should use "It must never be said," as shown in option 1.

3. Don’t say that he was ungenerous. (Incorrect) This option is still in the active voice and does not use the correct passive form. It retains the original active construction "Don't say" and does not convey the same meaning as the original sentence. The correct form should use the passive voice, as shown in option 1.

4. You must never say that he was being ungenerous. (Incorrect) This option changes the verb tense to "was being ungenerous," which is not the same as the original sentence ("he was ungenerous"). The correct form should use "It must never be said," as shown in option 1.