《资治通鉴·后晋纪·后晋纪一》
契丹主便依从了他，指着帐前的石头对赵德钧的使者说： 我已经许诺了石郎，除非这块石头烂了，才能改变。 
契丹主乃从之，指帐前石谓德钧使者曰： 我已许石郎，此石烂，可改矣！ 
The Khitan sovereign thus followed his advice and pointed at a stone in front of his tent and said to Zhao Dejun's envoy: I have already made a promise to that gentleman Stone, and unless this stone decays, it cannot be changed.
<s>[INST] Explain the meaning of this Classical Chinese passage in English: 契丹主乃从之，指帐前石谓德钧使者曰： 我已许石郎，此石烂，可改矣！  [/INST] The Khitan sovereign thus followed his advice and pointed at a stone in front of his tent and said to Zhao Dejun's envoy: I have already made a promise to that gentleman Stone, and unless this stone decays, it cannot be changed.</s>
Explain the meaning of this Classical Chinese passage in English: 契丹主乃从之，指帐前石谓德钧使者曰： 我已许石郎，此石烂，可改矣！
user
The Khitan sovereign thus followed his advice and pointed at a stone in front of his tent and said to Zhao Dejun's envoy: I have already made a promise to that gentleman Stone, and unless this stone decays, it cannot be changed.
assistant