Investment in business where bribe is given to take work

Asalam O Alikum By grace of Allah i have a good business of my own. Many years ago one good friend of my who now lives in a different city wanted to start a construction business but he didn’t had enough money to do business. I had agreement with him that i will become sleeping partner in his business and invest money in his business. He gives me profit return according to our agreed terms. He also does work of good quality of customers but recently i came to know from some people that he takes construction contracts by giving commission. But there is no confirmation of this since we both are in different cities and i never interfered in business since I’m already busy in my own work. Currently I’m confused is the profit which im getting Halal or not? And also have no idea how to talk about this with him because this can also break our friendship.