Reference for Bekhorot 59:12

שביעית לא בעיא חומה מעשר כיון דבעי חומה חמיר ליה:

ONE WHO IS SUSPECTED OF IGNORING TITHES IS NOT SUSPECTED OF IGNORING [ALSO] THE SABBATICAL YEAR'ONE WHO IS SUSPECTED OF IGNORING BOTH IS SUSPECTED OF IGNORING THE RULES OF LEVITICAL PURITY.

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