In لَا يُلْدَغُ الْمُؤْمِنُ, لَا negates the verb. يُلْدَغُ is passive, so the person stung is mentioned without naming what stung them.
لَا يَدْخُلُ uses an active verb, whereas لَا يُلْدَغُ uses a passive verb. In both, لَا negates, but the form and sense of the verb differ.
Compare the meanings:
يَدْخُلُ — he enters.
يُلْدَغُ — he is stung.
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Warnings about Paradise, People’s Rights, and Negative lā (Hadith 126–130)
In لَا يُلْدَغُ الْمُؤْمِنُ, لَا negates the verb. يُلْدَغُ is passive, so the person stung is mentioned without naming what stung them.
لَا يَدْخُلُ uses an active verb, whereas لَا يُلْدَغُ uses a passive verb. In both, لَا negates, but the form and sense of the verb differ.
Compare the meanings:
يَدْخُلُ — he enters.
يُلْدَغُ — he is stung.