Abdullah bin Buraydah said that two brothers, a Jew and a Muslim, took their dispute to Yahya bin Ya'mar. Yahya made the Muslim the heir and said: Abu al-Aswad told me that a man told him that Sayyiduna Mu'adh (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Islam increases and does not decrease." So he made the Muslim the heir.
If the report is sound, its interpretation is other than what he took it to mean: he only meant that Islam is ever increasing and is not diminished by apostasy. And this (in its chain) is an unknown man, so it is munqati' (broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12465