(a) It is narrated from Abu al-Ala, the freed slave of the Aslam, that he said: I saw Sayyiduna Ali (may Allah be pleased with him); he used to tie his waist-wrapper above the navel.
(b) This narration does not contradict (the view) that the navel is not awrah, because he tied the waist-wrapper above the navel only so that it would enclose the whole awrah. 'Wa billahi al-tawfiq' (And success is only through Allah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3249