ENOfficial
Mu'adh b. Jabal reported that God’s messenger said to him, “The keys of paradise are the testimony that there is no god but God.” Ahmad transmitted it.
Source: sunnah.com
Other translations
Arabic
عَن مُعَاذِ بْنِ جَبَلٍ قَالَ: «قَالَ لِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَفَاتِيحُ الْجَنَّةِ شَهَادَةُ أَنْ لَا إِلَه إِلَّا الله» . رَوَاهُ أَحْمد
sunnah.com