مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3529
Musnad of Abdullah bin Mas'ood
It was narrated that Abu Wa'il said: Ibn Mas'ood (رضي الله عنه) said: There are two things, one of which I heard from the Messenger of Allah (ﷺ) and the other is from myself (i.e., I worked it out myself): "Whoever dies ascribing a rival to Allah will enter Hell.” And I say: whoever dies not ascribing any rival to Allah or associating anything with Him, will enter Paradise.
Musnad Ahmad 3552Its isnad is saheeh]