Ein Ashan Beli Esh - אֵין עָשָׁן בְּלִי אֵשׁ
Pronunciation: Ein a·shan be·li esh
Literal translation: No smoke without fire, 'Where there's smoke, there's fire'
Tonight begins the Jewish holiday of Lag Ba'Omer which usually includes a large bonfire. So on that note...
You will find that many common proverbs in English are also said in Hebrew as well. This phrase is used to say that if unpleasant things are said about someone or something, there is probably a good reason for it.