Then the Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: "If a person performing ghusl for janabah finds wetness on the tip of his penis or senses the discharge of something after completing his ghusl, then if he had performed istibra’ as described earlier - through urination or proper effort - there is no need for him to perform wudu or repeat the ghusl, as this may only be pre-seminal fluid (wadi or madhy), which does not invalidate the state of purity. However, if he did not perform istibra’ as explained, then he must repeat the ghusl." This ruling is supported by the related evidence.
Commentary #34