The Messenger (sallal-laahu-alayhi-wasallam) said:
فإنه من يعش منكم فسيرى اختلافا، فعليكم بسنتي
‘’Indeed the one who lives long amongst you will see differences; so upon you is to (adhere) to my Sunnah.’’
Imaam Abu Haatim (rahimahullaah) said: This is clear evidence that the Messenger (sallal-laahu-alayhi-sallam) commanded his Ummah to know the Du’afaa amongst them and (distinguish) them from the Thiqaat. That is because the Sunnah cannot be adhered to alongside the lies and falsehood mixed with it, except by way of knowing the Du’afaa and (distinguishing them) from the Thiqaat.
[Source: Muqaddimah Kitaab Al-Majrooheem Minal Muhadditheen of Imaam Ibn Hibbaan (rahimahullaah) Page: 66]