Ibn Abdul-Barr (rahimahullaah) said:
According to the scholars, Taqleed (i.e. blind following) is other than Ittibaa. That is because Ittibaa is to follow a person based on what is apparent to you based on the superiority of his statement and soundness of his school of thought. And Taqleed is that you speak with his statement, whilst you neither know the angle of his speech nor its meaning and you reject speech besides it; or his mistake is made manifest to you, but you follow him and venerate his opposition (to the truth), whilst the corruptness of his speech is clear to you. This is what is forbidden to speak with in the religion of Allaah (The Most High).
[Jaami Bayaan Al-Ilm Wa-Fadlihee: 2/787]
Abu Mu’aawiyah (Abdullah Al-Gambi)