In Jainism there is no universal, fixed ban that says you must not mix yogurt and dal. The dietary rules are not single, rigid commandments but come from a combination of vows, seasonal observances, and local traditions.

Key points to understand:

• Jains follow ahimsa (non‑violence) and strive to minimize harm to all living beings. This leads to many restrictions (like avoiding root vegetables, certain ferments, etc.) that vary by community and practice. But there isn’t a standard rule that forbids yogurt with dal everywhere.
• Some strict observances (like Ayambil days or specific religious periods) encourage very minimal, simple foods and may treat certain combinations as less suitable for that time. But these are practices for certain days or vows, not universal doctrine.
• Differences between Digambar and Shwetambar communities exist in many rituals and dietary nuances, but a blanket prohibition on dahi+dal is not a canonical, universally applied rule in either tradition.

In short, yogurt with dal is not always disallowed in Jainism; its acceptability depends on local tradition, the specific vow you are following, and the season or observance you are keeping.

You can read more about Jain dietary principles and related practices here