Al Salamu 'Alaykum.
Ibn al Qayyim said in his aforementioned book ('Ilam al Muwaqqi'in):
Al Sha'bi said: "Whoever it pleases to have confidence in issuing decrees (qada'), let him take the opinion of 'Umar."
Mujahid said: "When people differ in anything, look at what 'Umar did and adopt it."
These are clear texts from al-Sha'bi and Mujahid on taqlid.
Ibn al Qayyim said in his aforementioned book:
Tawus said: "I met seventy of the Companions of Allah's Messenger (saws) and when they disagreed on something, they would stop at the opinion of Ibn 'Abbas."
Muhammad ibn Jarir said: "There was none (among the Sahaba) who had known companions who codified his fatwa and his positions in fiqh (jurisprudence) besides Ibn Mas'ud and he would leave his position and his opinion in favor of the opinion of 'Umar and he would (at times) come close to differing with him in some of his positions and would then go back on his own opinion in favor of his opinion."
Al-Sha'bi said: "`Abdullah would not perform qunut" (supplication) [in the Fajr prayer], and he said: "Had 'Umar performed Qunut, `Abdullah would have performed Qunut."
He also said:
Al-A'mash said regarding Ibrahim [al-Nakha'i]: "He would not divert from the opinion of 'Umar and `Abdullah (ibn Mas'ud) when they agreed and when they disagreed, the opinion of 'Abdullah was more appealing to him because it was more subtle."
He said on page 5:
Those of the Companions of Allah's Messenger (saws) from whom fatwa was preserved are some one hundred and thirty souls that range between men and women and the mukhthirun (those who issued fatwa in large numbers) from them are seven: 'Umar ibn al Khattab, 'Ali ibn Abi Talib, 'Abdullah ibn Mas'ud, A'isha, mother of the believers, Zayd ibn Thabit, 'Abdullah ibn 'Abbas and 'Abdullah ibn 'Umar.
These texts show you the way of taqlid was prevalent amongst the Sahaba and Tabi'in to such a degree that some mujtahids imitated some others from them, let alone those unqualified for ijtihad. Rather, the Prophet (saws) instructed them to do taqlid when he commanded them to follow the Sunnah of the righteous Caliphs. Rather, Allah commanded them to do taqlid when He said: "Ask the People of Remembrance if you do know know." (16:43)
Thus, the statement that taqlid is an innovation (bid'ah) that appeared in the fourth century or an innovation that appeared in the sixth century is concealment of the truth (kitman) and the truth is that taqlid is an inherited practice from the time of Allah's Messenger (saws) to this time of ours, and is established from the texts some of which we cited and some of which we left out, fearing prolixity.
Taken from Al Din al Qayyim of 'Allama Habib Ahmad Kairanwi.