Below is a collection of Ahadith in which the Imams (as) have advised/warned against rejection of Ahadith attributed to them.

Hadith 1:

In a lengthy hadith, Imam Moosa Kazim (as) says the following in one of his letters,

ووال آل محمد ولا تقل لما بلغك عنا ونسب إلينا هذا باطل وإن كنت تعرف منا خلافه فإنك لا تدري لما قلناه وعلى أي وجه وصفناه

"Accept wilayah of Ale (family of) Mohammed and do not say about what has reached you from us or is ascribed to us as false even though you may know something from Us which is against it, because you do not know why we said it and how we explained it."

[Source: Al-Kafi. Vol. 8, Pg. 124, H. 95]

Hadith 2:

أَبِي (رحمه الله) قَالَ حَدَّثَنَا سَعْدُ بْنُ عَبْدِ اللَّهِ عَنْ أَحْمَدَ بْنِ أَبِي عَبْدِ اللَّهِ عَنْ مُحَمَّدِ بْنِ إِسْمَاعِيلَ بْنِ بَزِيعٍ عَنْ جَعْفَرِ بْنِ بَشِيرٍ عَنْ أَبِي حُصَيْنٍ عَنْ أَبِي بَصِيرٍ عَنْ أَحَدِهِمَا (ع) قَالُوا لَا تُكَذِّبُوا بِحَدِيثٍ أَتَاكُمْ بِهِ مُرْجِئِيٌّ وَ لَا قَدَرِيٌّ وَ لَا خَارِجِيٌّ نَسَبَهُ إِلَيْنَا فَإِنَّكُمْ لَا تَدْرُونَ لَعَلَّهُ شَيْءٌ مِنَ الْحَقِّ فَتُكَذِّبُوا اللَّهَ عَزَّ وَ جَلَّ فَوْقَ عَرْشِهِ

From Abu Basir, from one of the two Imams (as), who said,

"Do not deny a hadith that reaches to you through a Murji, a Qadri or a khariji that he attributes to Us, since you would not know that it could be from the truth and hence you would result in having denied Allah above His throne. "

[Source: Ilal al-Shara'i, Shaikh Sadooq, Vol. 2, Pg. 395]

Hadith 3:

حَدَّثَنَا أَحْمَدُ بْنُ مُحَمَّدِ بْنِ عِيسَى، عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ وَ مُحَمَّدِ بْنِ خَالِدٍ الْبَرْقِيِّ، عَنْ عَبْدِ اللَّهِ بْنِ جُنْدَبٍ، عَنْ سُفْيَانَ بْنِ السِّمْطِ، قَالَ: قُلْتُ لِأَبِي عَبْدِ اللَّهِ ع: جُعِلْتُ فِدَاكَ يَأْتِينَا الرَّجُلُ مِنْ قِبَلِكُمْ يُعْرَفُ بِالْكَذِبِ فَيُحَدِّثُ بِالْحَدِيثِ فَنَسْتَبْشِعُهُ.

فَقَالَ أَبُو عَبْدِ اللَّهِ ع: «يَقُولُ لَكَ: إِنِّي قُلْتُ الليل [لِلَّيْلِ‌] إِنَّهُ نَهَارٌ، وَ النهار [لِلنَّهَارِ] إِنَّهُ لَيْلٌ؟» قُلْتُ: لَا، قَالَ: «فَإِنْ قَالَ لَكَ هَذَا إِنِّي قُلْتُهُ فَلَا تُكَذِّبْ بِهِ، فَإِنَّكَ إِنَّمَا تُكَذِّبُنِي

From Sufyan bin Samt, who said: I said to Imam al-Sadiq (as), "May I be sacrificed for you. Sometimes someone known for lying comes to us and narrates a Hadith, after which we are disgusted."

Imam al-Sadiq (as) said: "Did he say to you that I said that the night is the day and that the day is night?"

I said: "No."

Imam (as) said, "If he says to that I have said this, then don't deny it , or you will as a result deny me."

[Source: Mukhtasar Basair al-Darajaat, Pg. 233]

Hadith 4:

عَنْهُ عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ مَحْبُوبٍ عَنْ جَمِيلِ بْنِ صَالِحٍ عَنْ أَبِي عُبَيْدَةَ الْحَذَّاءِ قَالَ سَمِعْتُ أَبَا جَعْفَرٍ (عَلَيهِ السَّلام) يَقُولُ وَالله إِنَّ أَحَبَّ أَصْحَابِي إِلَيَّ أَوْرَعُهُمْ وَأَفْقَهُهُمْ وَأَكْتَمُهُمْ لِحَدِيثِنَا وَإِنَّ أَسْوَأَهُمْ عِنْدِي حَالاً وَأَمْقَتَهُمْ لَلَّذِي إِذَا سَمِعَ الْحَدِيثَ يُنْسَبُ إِلَيْنَا وَيُرْوَى عَنَّا فَلَمْ يَقْبَلْهُ اشْمَأَزَّ مِنْهُ وَجَحَدَهُ وَكَفَّرَ مَنْ دَانَ بِهِ وَهُوَ لا يَدْرِي لَعَلَّ الْحَدِيثَ مِنْ عِنْدِنَا خَرَجَ وَإِلَيْنَا أُسْنِدَ فَيَكُونَ بِذَلِكَ خَارِجاً عَنْ وَلايَتِنَا

Narrated that Abu Jafar Imam Baqir (ع) said,

"By Allah, the most beloved to Me of My companions are most restraining from the worldly attractions, most knowledgeable in Fiqh (laws of Sharia) and most secretive in our Hadith. Of the worst conditions among them and most disliked is the one who upon hearing the Hadith that is ascribed it to Us and narrated it from Us, does not accept it, detesting it and rejecting it and considering as disbelievers those to accept the Hadith, while he does not know that perhaps the Hadith has come out from Us and is traced back to Us and as a result of this he will be out of our Walayah (guardianship)."

[Source: al-Kafi, Vol. 2, Pg. 223]

Hadith 5:

In this hadith Imam Sadiq (as) is seen praising a person who submits to everything that comes from the Imams (as).

مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ حَمَّادِ بْنِ عِيسَى عَنِ الْحُسَيْنِ بْنِ الْمُخْتَارِ عَنْ زَيْدٍ الشَّحَّامِ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ السَّلام) قَالَ قُلْتُ لَهُ إِنَّ عِنْدَنَا رَجُلاً يُقَالُ لَهُ كُلَيْبٌ فَلا يَجِي‏ءُ عَنْكُمْ شَيْ‏ءٌ إِلا قَالَ أَنَا أُسَلِّمُ فَسَمَّيْنَاهُ كُلَيْبَ تَسْلِيمٍ قَالَ فَتَرَحَّمَ عَلَيْهِ ثُمَّ قَالَ أَ تَدْرُونَ مَا التَّسْلِيمُ فَسَكَتْنَا فَقَالَ هُوَ وَالله الاخْبَاتُ قَوْلُ الله عَزَّ وَجَلَّ الَّذِينَ آمَنُوا وَعَمِلُوا الصَّالِحاتِ وَأَخْبَتُوا إِلى‏ رَبِّهِمْ

Narrated from Zayd al-Shahham who said,

“I said to Abu Abdallah Imam Sadiq (as), ‘Among us there is a man called Kulayb. Nothing comes from you but that he says, “I submit to it.” Thus, we call him, “Kulayb, the submissive.”

The Imam (as) prayed for Mercy on him (Tarahham) and then the Imam (as) said, “Do you know what submission is?”

We remained silent. The Imam (as) said, “That, by Allah, is al-Ikhbat (humbleness) in the words of Allah (عز و جل), "Those who believe and do righteous deeds and are humble before their Lord." (11:23)

[Source: al-Kafi, Vol.1, Pg. 390-391, Hadith. 3]