It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) was asked about the reward of ribat (guarding the frontier), and he (peace and blessings be upon him) said: "Whoever guards the frontier for one night as a sentry behind the Muslims will receive a reward equal to the reward of all those behind him, that is, equal to those who fast and those who pray."
Hadith Referenceالمعجم الأوسط / باب الميم / 8059
Hadith Gradingمحدثین:رجاله ثقات
Hadith Takhrij«قال الهيثمي: رواه الطبراني في الأوسط ورجاله ثقات «مجمع الزوائد ومنبع الفوائد، ج 5، ص 289»»