Is a partner entitled to add a debt amount (that was paid from the business's income) to his share in the capital, and how would the Sharia-compliant division of the return be in this case?

The original agreement in the company is not invalidated by subsequent actions. There are three possibilities to explain the matter:

1. First Possibility: Your relative borrowed 6,0 to be from his share, making your share 17,0 and his share 10,0. His repayment of these 6,0 from the gross income is an injustice to you. The 6,0 are his debt to be repaid from the profit. Your share would be 62.96% and his share 37.4%. 2. Second Possibility: You both agreed that the company capital is 21,0 (17,0 for you and 4,0 for him), and the remainder is to be paid from the gross income. He is not allowed to add the 6,0 to his share; rather, it remains from the profit. Your share would be 80.95% and his share 19.5%. 3. Third Possibility: The agreement was that the 6,0 is shared between you (3,0 from you and 3,0 from him), making your share 20,0 and his share 7,0. Repaying it from the gross profit is an injustice to you. Each of you is required to bring 3,0, and it is added to the profit. Your share would be 74.7% and his share 25.93%.

The principle is that contracts are based on mutual consent, in compliance with the words of Allah the Almighty: "O you who have believed, fulfill [all] contracts" [Al-Ma'idah: 1] and "And fulfill [every] commitment. Indeed, every commitment will be questioned about" [Al-Isra: 34], and with the words of the Prophet, peace be upon him: "Muslims are bound by their conditions." The distribution of returns should be according to each partner's capital ratio.