按甲休兵

Yojijukugo (四字熟語), from 按甲(あんこう) (ankō, “remove one's armor”) + 休兵(きゅうへい) (kyūhei, “rest one's troops”).

Derived from the Shiji, in the form 案甲休兵, using the variant form 案 in place of 按, from the chapter named 淮陰侯列傳:

廣武君對曰：『方今爲將軍計，莫如案甲休兵，鎮趙撫其孤… [MSC, trad.]

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广武君对曰：『方今为将军计，莫如案甲休兵，镇赵抚其孤… [MSC, simp.]

Guǎngwǔ jūn duì yuē: ‘Fāng jīn wèi jiāngjūn jì, mòrú ànjiǎxiūbīng, zhèn zhào fǔ qí gū... [Pinyin]

Lord Guanwu replied: “At present, the better course of action for Your Excellency would be to put down your armor and rest your soldiers, pacify Zhou and take care of its orphaned king…”

The current form, 按甲休兵, can be found in the Book of Han, 韓彭英盧吳傳:

廣武君對曰：『當今之計，不如按甲休兵…』 [MSC, trad.]

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广武君对曰：『当今之计，不如按甲休兵…』 [MSC, simp.]

guǎngwǔ jūn duì yuē: ‘Dāng jīn zhī jì, bùrú ànjiǎxiūbīng...’ [Pinyin]

Lord Guanwu responded: “The course of action at present would best be to put down your armor and rest your soldiers…”

按(あん)甲(こう)休(きゅう)兵(へい) • (ankō kyūhei) 

1. to stop fighting; to suspend hostilities; to cease combat operations; to sign an armistice; to agree to a cease-fire; to call a truce

• 按甲(あんこう)寝兵(しんぺい) (ankō shinpei)

• “按甲休兵”, in 漢検四字熟語辞典 (Kanken Yojijukugo Jiten, “Kanji Kentei Four-Character-Idiom Dictionary”) (in Japanese), second edition, Tōkyō: Japan Kanji Aptitude Testing Foundation, 2012, →ISBN, page 65