Fourfold Assembly of the Buddha wall mural behind the great reclining Buddha image in the Hall of the Reclining Buddha (Viharn Phranon) at Wat Pho (Ayutthayan Period Monastery Wat Bodharam) in Bangkok. Restored by King Rama III and his son Prince Laddawan.
The degree to which the existence of the Bhikkhuni Sangha is an integral requirement for the welfare of the Buddha Sasana and for its stability is highlighted in a teaching of the Buddha’s in the Samyutta Nikaya. This teaching points out that for ensuring the healthy and long duration of the Dhamma and for preventing its disappearance, all four assemblies, including the bhikkhunis, should live with respect towards the Buddha, the Dhamma, the Sangha, the Discipline and the development of Samadhi. This passage thus treats the existence of bhikkhunis, and of all four assemblies practicing well, as an integral requirement for the welfare and stability of the Buddha Sasana.
[SN 16.13 at SN II 225,8: bhikkhu bhikkhuniyo upasaka upasikayo satthari … dhamme … sa ghe … sikkhaya …samadhismi sagarava viharanti sappaissa. Ime kho … pañca dhamma saddhammassa hitiya asammosaya anantaradhanaya sa vattanti.]