What degree of illness permits the joining (Jam'u) of prayers?

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The illness that permits the joining of prayers is that which imposes hardship and weakness upon the afflicted person when performing each prayer at its designated time. Imam Ahmad ibn Hanbal indicated that he hopes it is permissible for the sick person to join prayers if they are weak and unable to perform them separately. This ruling also applies to a woman experiencing persistent vaginal bleeding (Mustahadah) and one suffering from involuntary urine leakage (salis al-bawl), and those in a similar condition, based upon the established Hadith evidence.