Allah, the Blessed and Exalted, says: "They ask you for a ruling. Say: Allah gives you a ruling concerning kalalah: if a man dies having no child and he has a sister, she will have half of what he left; and he (the brother) will inherit from her if she has no child. But if there are two (sisters), they will have two-thirds of what he left." [Surah al-Nisa: 176]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / Q12325