It is narrated from Salamah bin Sabrah (may Allah have mercy on him) that Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) addressed us in a sermon and said: "You are the complete believers and you are the people of Paradise, and I strongly hope that those of Persia and Rome whom you gain (under the influence of Islam) will also enter Paradise, for when one of them does a good deed you say (in encouragement): 'Ahsanta, yarhamuka Allah' (You have done well, may Allah have mercy on you), and you say: 'Ahsanta, baraka Allahu fik' (You have done excellently, may Allah bless you). And Allah, the Mighty and Majestic, says: 'And He responds to those who believe and do righteous deeds, and gives them more out of His bounty' [Surah al-Shura: 26]."
Imam Musaddad related this statement in his Musnad, and there are supporting reports for it in other books of hadith.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب التفسير / 3706
Hadith Gradingمحدثین:إسناده ضعيف
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :إسناده ضعيف » «أخرجه المستدرك للحاكم برقم: 3682، وأخرجه مصنف ابن أبي شيبة برقم: 31022»