Hadith 1:

حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ عَنْ مُحَمَّدِ بْنِ عِيسَى عَنْ عَبْدِي يَرْفَعُهُ إِلَى أَبِي عَبْدِ اللَّهِ ع قَالَ: أَبَى اللَّهُ أَنْ يُجْرِيَ الْأَشْيَاءَ إِلَّا بِالْأَسْبَابِ فَجَعَلَ لِكُلِّ شَيْ‏ءٍ سَبَباً وَ جَعَلَ لِكُلِّ سَبَبٍ شَرْحاً وَ جَعَلَ لِكُلِّ شَرْحٍ مِفْتَاحاً وَ جَعَلَ لِكُلِ‏ مِفْتَاحٍ‏ عِلْماً وَ جَعَلَ لِكُلِّ عِلْمٍ بَاباً نَاطِقاً مَنْ عَرَفَهُ عَرَفَ اللَّهَ وَ مَنْ أَنْكَرَهُ أَنْكَرَ اللَّهَ ذَلِكَ رَسُولُ اللَّهِ ص وَ نَحْن‏

Narrated that AbU Abdillah Imam Sadiq (ع) said,

"Allah (عز وجل) refuses to implement (carry out) anything without a reason and so He has made a reason for everything and has made explanation for every reason and has made key for every explanation, and has made knowledge for every key and for every knowledge he has made speaking door, The one who recognizes Him (the speaking door) recognizes Allah and the one who rejects Him rejects Allah. That (speaking door) is Prophet of Allah (ص) and Us."

[Source: Basair al-Darajaat, Pg. 26]

Hadith 2:

عَلِيُّ بْنُ مُحَمَّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ مُوسَى بْنِ الْقَاسِمِ بْنِ مُعَاوِيَةَ وَمُحَمَّدُ بْنُ يَحْيَى عَنِ الْعَمْرَكِيِّ بْنِ عَلِيٍّ جَمِيعاً عَنْ عَلِيِّ بْنِ جَعْفَرٍ عَنْ أَبِي الْحَسَنِ مُوسَى (عَلَيْهِ السَّلام) قَالَ قَالَ أَبُو عَبْدِ الله (عَلَيْهِ السَّلام) إِنَّ الله عَزَّ وَجَلَّ خَلَقَنَا فَأَحْسَنَ خَلْقَنَا وَصَوَّرَنَا فَأَحْسَنَ صُوَرَنَا وَجَعَلَنَا خُزَّانَهُ فِي سَمَائِهِ وَأَرْضِهِ وَلَنَا نَطَقَتِ الشَّجَرَةُ وَبِعِبَادَتِنَا عُبِدَ الله عَزَّ وَجَلَّ وَلَوْلانَا مَا عُبِدَ الله

Narrated that Abu al-Hasan Imam Kazim (ع) said,

"Surely Allah (عز وجل) created Us and He made Our creation the best. He formed Us and made Our form the best. He made Us the treasurers of His in His heavens and His earth. For Us the tree spoke and through Our worship Him Allah (عز وجل) is worshipped. Had we not been in existence Allah (عز وجل) would not have been worshipped."

[Source: al-Kafi, Vol. 1, Pg. 193]

Hadith 3:

حدثنا احمد عن الحسين بن راشد عن موسى بن القسم عن علي بن جعفر عن أخيه قال قال أبو عبد الله ان الله خلقنا فأحسن خلقنا وصورنا فأحسن صورنا فجعلنا خزانه في سماواته وارضه ولولانا ما عرف الله

Narrated that Abu Abdillah Imam Sadiq (ع) said,

"Surely Allah (عز وجل) created Us and He made Our creation the best. He formed Us and made Our form the best. He made Us the treasurers of His in His heavens and His earth. Had We not been in existence Allah (عز وجل)  would not have been known."

[Source: Basair al-Darajaat, Pg. 125]

Hadith 4:

حدثنا علي بن محمد عن القسم بن محمد عن سليمان بن داود المنقري عن سفيان بن موسى عن سدير عن أبي جعفر عليه السلام قال سمعته يقول نحن خزان الله في الدنيا والآخرة وشيعتنا خزاننا ولولانا ما عرف الله

Narrated that Abu Jafar Imam Baqir (ع) said,

"We are the Treasurers for Allah (عز وجل) in the World and the Hereafter, and Our followers (shia) are treasurers for Us. And were it not for Us, Allah (عز وجل) would not have been known."

[Source: Basaair Al-Darajat Pg. 125]

Hadith 5:

الحسين بن محمد، عن معلى بن محمد، عن محمد بن جمهور، عن علي بن الصلت، عن الحكم وإسماعيل ابني حبيب، عن بريد العجلي قال: سمعت أبا جعفر عليه السلام يقول: بنا عبد الله، وبنا عرف الله، وبنا وحد الله تبارك وتعالى، ومحمد حجاب الله تبارك وتعالى

Narrated that Abu Jafar Imam Baqir (عليه السلام) said,

“Through Us Allah is worshipped. And through Us Allah is known. And Through Us belief in the Oneness of Allah (تبارك وتعالى) is established. And Muhammad (صلى الله عليه وآله) is the veil (Hijab) of Allah (تبارك وتعالى).”

[Source: al-Kafi, Vol. 1, Pg. 145]

Explaining the last words of the hadith, Allamah Majlisi says:

ومحمد حجاب الله ، أي واسطة بين الله وبين خلقه

“And Muhammad (صلى الله عليه وآله) is the Veil (Hijab) of Allah – Meaning that He is the means/intermediary between Allah and His creations.”

[Source: Mirat al-Uqul, Vol. 2, Pg. 121]