بسم الله الرحمن الرحيم
‘Ujub (عُجب) in Arabic denotes conceitedness, marveling and being impressed or amazed with oneself, as well as attributing excellence to one’s own ability; especially when performing good deeds. It is something blameworthy that annuls good deeds and invites the displeasure of Allah because it entails lack of sincerity.
Ibn al-Qayyim said: لا شيء أفسد للعمل الصالح من العُجب ورؤية النفس
Nothing corrupts one’s righteous deeds than seeing wonder and being amazed with one’s self (i.e. ujub).” 
Imam An-Nawawi is said, ❝Know, that sincerity is often affected by the disease of ‘ujub. Whoever has ‘ujub when giving charity, then his charity is erased. Similarly, people who boast about being charitable, then their charity is erased.❞ 
In pointing out some of the ways to remove any risk of ujub in our deeds, shaykh ‘Abd Al-Azeez At-Tarifi mentioned something important. Strengthening our spiritual connection with Allah will translate into physical discernment when performing righteous tasks as any need to impress or rely upon other humans will diminish completely. He said:
عبادة الخفاء تزيد من إخلاص العبد وصدقه، وتكسر عُجبه بعمله، وتُقوّي صلته بربه وتوكله عليه، فمن اختفى بعمله عن الخلق تجرّد للخالق
“Worship in secret increase the sincerity of the slave (of Allah) and reflects his truthfulness, and reduces ‘ujub. It strengthens the connection with our Rabb and renders tawwakul to him; so whoever conceals his deeds from the creation, will be freed (from the need of others) by the Creator. ” 
Allah Mentions in numerous places in Surat Al-Zumar and Al-Ghafir,
إِنَّا أَنزَلْنَا إِلَيْكَ الْكِتَابَ بِالْحَقِّ فَاعْبُدِ اللَّهَ مُخْلِصًا لَّهُ الدِّينَ
“Indeed, We have sent down to you the Book, [O Muhammad], in truth. So worship Allah being sincere to Him in religion.” 
May Allah cure us from the malady of ‘ujub. Ameen.
 see ‘Ta’theer al-Anfaas bi dhikr Hadeeth al-Ikhlas’, p. 584
 سطور: من النقل والعقل والفكر
 Al-Zumar, 2 [see also, Al-Zumar 11, 14 and Al-Ghafir, 14, 65 & others]