Undesirability of Entering the Mosque after Eating raw Onion or Garlic

Riyad-us-Saliheen 1702
Anas (May Allah be pleased with him) said: The Prophet (PBUH) said, "He who has eaten from this plant (i.e., garlic) should not approach us and should not offer Salat (prayer) along with us."

[Al-Bukhari and Muslim]