Answered by Shaykh Faraz Rabbani
I run a limousine business and I dont provide alcohol but if customers bring their own and drink it in the limousine, does that make my earning haram?

In the Name of Allah, Most Merciful and Compassionate
May Allah’s peace and blessings be upon His Messenger Muhammad, his folk, companions, and followers
Since the service you yourself are providing–the limousine service–is in itself permissible, then both your work and earnings are permissible and halal. [As understood from Ibn Abidin’s Radd al-Muhtar] However, it would not be permitted to encourage customers, whether explictly or implicitly, to bring their own alcohol.
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Wassalam,
Faraz Rabbani