Imam al-Shafi'i (may Allah have mercy on him) said: "So whoever establishes proof (testimony) for any of it (the goods), it is his; and whoever does not establish proof, then the analogy, which in my view no one is excused for overlooking, based on consensus, is that these goods are in the joint possession of both of them. So each of them will swear an oath against his companion's claim, and if both swear, it (the goods) will be divided between them half and half."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الدعوى والبينات / Q21295