Short answer: It is not a universal ban in Jainism to eat dahi (curd) with dal. Acceptability depends on your local tradition, vows, and the season.

• General principle: Jains follow ahimsa (non-violence) and avoid foods that involve harming tiny life-forms. This leads to different dietary practices across communities.
• Dairy and curd: Many Jains prefer not to eat fermented dairy like curd because fermentation involves microorganisms. Some households also avoid curd on certain days or during strict vows.
• Dal/dahi combo: Since dal is a plant-based protein and dahi is dairy, some communities allow it, while stricter practices (especially during periods like Paryushan or Ayambil days) may discourage or prohibit dairy or fermented foods.
• Digambar vs. Shwetambar: There are differences in how strictly dairy and fermentation are treated. Always check with your local guru or community for your tradition’s guidance.

You can read more about dietary considerations and curd in Jainism here and about the nuance on yogurt/dal combinations here .

If you want, tell me your specific tradition (Digambar or Shwetambar) or the occasion (regular day vs. Paryushan), and I’ll tailor the guidance.