Sayyidah Aishah (may Allah be pleased with her) was asked about the muhrim wearing a himyan (a money belt), and she said: What harm is there in it? (It is) so that he may keep his spending money secure.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9186
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: The muhrim has been given a concession to wear a himyan (money belt) and a ring.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9187