《黄帝内经·素问·六元正纪大论》
三之气，主气为少阳相火，客气亦为少阳相火，主客气同，司天之气施布政令，炎暑乃至，少阳相火上临，火气过甚，故雨水穷尽而不降。
三之气，天政布，炎暑至，少阳临上，雨乃涯。
The three Qi, the principal Qi is the Shao Yang minister fire, and the guest Qi is also the Shao Yang minister fire. The principal and guest Qi are the same, and they control the Qi of heaven's orders. When the heat of summer arrives, the Shao Yang minister fire rises, and the fire Qi is too strong, so the rain stops falling.