Two persons agreed to hold a partnership with a variable share in the capital
If the reality is as you have mentioned, there is no impediment to you participating with this person, if his business is free from Riba (usury/interest), for whatever period you agree upon, because
the origin in transactions (Part No. 11; Page No. 163) is that they are lawful unless there is any proof of prevention. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.