Sayyiduna Abu Hurairah (may Allah be pleased with him) narrated from the Messenger of Allah (peace and blessings be upon him), he (peace be upon him) said: "Whoever brings a good deed will have a reward better than it, and they (the righteous) will be safe from the terror of that Day." He said: That (good deed) is «لا الهٰ الا الله», and whoever brings an evil (sin), their faces will be thrown down into Hellfire. He said: "That (sin) is shirk (associating partners with Allah)."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الايمان / 66
Benefits: ➊ In the mentioned hadith, the virtue of the statement of Tawhid (the declaration of Allah’s oneness) and the condemnation of shirk (associating partners with Allah) are described. ➋ Tawhid is a cause of success and honor in this world and the Hereafter. ➌ Shirk brings about failure in the Hereafter and humiliation and disgrace in both this world and the Hereafter. ➍ The people of faith, the people of Tawhid, are destined for Paradise, whereas the people of shirk are destined for Hellfire, and Paradise is forbidden for them.