如來有四不可思議之事，非小乘所能知。一世界不可思議，二眾生不可思議，三龍不可思議，四佛土境界不可思議。見增一阿含經十八。
The four indescribables, v. 增一阿含經 18, are the worlds; living beings; dragons (nagas); and the size of the Buddha-lands.
The four things of a Buddha which are beyond human conception: 世界 his world, 眾生 his living beings, 龍 his nāgas, and 佛土境界 the bounds of his Buddha-realm.
世界不可思議、眾生不可思議、龍不可思議、佛土境界不可思議。