There are different types of legitimate partnership in Islam. There forms of partnership are: al-`Anân, al-Mudârabah, al-Wujûh and al-Abdân.
If the form of partnership between the two of you is by each partner supplying half the capital and splitting the profits equally, then this would be a legitimate form of partnership in Islam. This is called an `Anân partnership.
The following guidelines must be observed:
The two shares in the capital investment must be known and fully disclosed. The profit that each party receives should be a certain fixed percentage such as a quarter, a half, a third, etc. Alternatively, the profit may be calculated according to the percentage contribution of each partner.
If these conditions are met, then this will be a legitimate partnership contract.