Saeed bin Musayyib says: "If it is flowing on my thighs, even then I will not end the prayer." The narrator named Sufyan states that what is meant by this is urine, that is, when a person is afflicted with illness.
Hadith Referenceسنن الدارقطني / كتاب الطهارة / 778
Hadith Takhrij«أخرجه مالك فى ((الموطأ)) برقم: 124، والدارقطني فى ((سننه)) برقم: 778، وعبد الرزاق فى ((مصنفه)) برقم: 613، 614»