If the reality is as you mentioned that one of the two partners pays the amount of the Zakah payable on his share and the profits generated from his investment, while the other does not, he will have fulfilled his religious obligation and it is hoped that he will be rewarded by Allah. He is not to blame for the fact that his partner does not pay the Zakah that is due on his share, or pays it merely to show off. However a God-fearing person who pays the Zakah due on his property should not continue in
a partnership with one who does not pay Zakah. Instead, he should advise his partner that he must pay the Zakah (Part No. 9; Page No. 406) and if he does not, he should end his business partnership with that person to avoid this evil.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.