Sayyidah Aishah (may Allah be pleased with her) said: "Allah and His Messenger (peace and blessings be upon him) are the guardian of one who has no guardian, and the maternal uncle is the heir of one who has no heir."
What is preserved (mahfuz) is that this is the saying of Aishah, mawquf (stopping) at her; Abd al-Razzaq likewise narrated it from Ibn Jurayj as mawquf. Abu Asim used to attribute it to the Prophet (peace and blessings be upon him) in some narrations from him, then he doubted it; so the marfu' version is not preserved, and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12215