Mishkat al-Masabih 36
‘Ubada b. as-Samit said:
I heard God's messenger say, “If anyone testifies that there is no god but God and that Muhammad is God's messenger, God will keep him from going to hell." 

Muslim transmitted it.
عَنْ عُبَادَةَ بْنِ الصَّامِتِ رَضِيَ اللَّهُ عَنْهُ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: «مَنْ شَهِدَ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ حَرَّمَ الله عَلَيْهِ النَّار»