To determine whether the discharge is impure (najis) and requires ghusl, consider the following:
1. The Nature of the Discharge:
If you reach the peak of desire but do not see the discharge at that moment, and then a few minutes later you notice some moisture, you should assess whether this moisture is semen (mani) or pure secretions that do not necessitate ghusl. The discharge must be significant enough to be classified as semen; however, it can also be a small amount. The key is to ascertain whether the discharge is indeed semen or just normal secretions.
For further guidance, refer to the relevant Islamic texts and jurisprudence.
2. The Amount of Discharge:
Generally, the discharge must be substantial to be considered semen. If it is a small amount, it may not necessitate ghusl. It is important to differentiate between the two types of discharge based on their characteristics and the context in which they occur.
For more detailed information, consult Islamic legal resources or scholars.