The Messenger of Allah ﷺ said, "Remembrance of Allah, the Exalted, in the path of Allah is multiplied above mere spending by seven hundred times." Yahya, in his version of the hadith, said, "By seven hundred thousand times."
حدثنا حسن حدثنا ابن لهيعة قال وحدثنا يحيى بن غيلان قال حدثنا رشدين عن زبان
عن رسول الله ﷺ قال إن الذكر في سبيل الله تعالى يضعف فوق النفقة بسبع مائة ضعف قال يحيى في حديثه بسبع مائة ألف ضعف
Its chain of transmission is daif because of Rushdin. It is found in Abu Dawud, 3/8, no. 2498, in the chapter on jihad. The weakening of the mention through the route of Zaban means it is hasan. It is also found in Bayhaqi, 9/172. All these hadiths are about encouragement to good deeds.