[Quote] Be aware of the supplication of the oppressed, O you who follows up the mistakes of the people!

The great scholar and Imam Ibn-ul-Qayyim, may Allah have mercy upon him, said:

"Beware, O you who follows up the faults and mistakes of those who differ with you, not to get hit by their supplication, for there is indeed no barrier between the supplication of the oppressed and Allah.

And take a lesson from what happened to the people who came before. Verily he is successful who takes heed by way of others.

​And here (for instance) we have Muhammad Ibn Abī-l-Faraj Al-Kitānī about whom was said that: "He used to follow up the mistakes of the scholars, and so they supplicated against him, and as a consequence he never became successful."

Translated by Salafi-Dawah.com.
Source: Madārij As-Sālikīn 1/197.

 قال إبن القيم رحمه الله تعالى

 واحذر أيها المتتبع لعثرات وعورات مخالفيك من أن تصيبك دعوتهم فإن دعوة المظلوم ليس بينها وبين الله حجاب واعتبر بما حصل لمن سبق فإن السعيد من وعظ بغيره فهذا محمد بن أبي الفرج الكتاني قيل فيه: إنه كان يتتبع عورات الشيوخ فدعوا عليه فلم يفلح 

 [مدارج السالكين ١/١٩٧]