Sayyiduna Abu al-Darda' (may Allah be pleased with him) reports that the Prophet (peace and blessings be upon him) said: "Standing guard for a month is better than fasting perpetually. Whoever dies while standing guard in the path of Allah will be safe from the Greatest Terror; he is provided with his provision and given the fragrance (or breeze) of Paradise, and the reward of a mujahid continues for him until Allah Almighty raises him again (on the Day of Resurrection)."
Al-Tabarani recorded it, and its narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجهاد / 9504