Hadees of the Imam's (as) is difficult

حدثنا محمد بن الحسين عن صفوان بن يحيى عن ذريح المحاربي و أحمد بن محمد عن البرقي عن صفوان عن ذريح قال

سمعت أبا عبد الله عليه السلام يقول إن أبى نعم الأب رحمة الله عليه كان يقول لو أجد ثلاثة رهط استودعهم العلم وهم أهل لذلك لحدثت بما لا يحتاج فيه إلى نظر في حلال ولا حرام وما يكون إلى يوم القيمة إن حديثنا صعب مستصعب لا يؤمن به الا عبد امتحن الله قلبه للأيمان

Narrated to me Muhammad bin Al-Husain, from Safwan bin Yahya, from Zareeh Al-Maharabi and Ahmad bin Muhammad, from Al-Baraqi, from Zareeh who said, I heard Aba Abdillah (as) say:

"Indeed by Father (as) was a good father, May Allah (swt) have mercy on Him. He used to say, "If I could find 3 people, I would entrust them the Knowledge and (If) they would be deserving of it. I would narrate to them with which they would not have any need in it in looking into the permissible and Prohibited and what will be until the day of Judgement. Indeed, Our Hadees are difficult and more difficult, none believe in them but a slave whose heart has been tested for faith by Allah (swt)."

[Source: Basaair Al-Darajaat, Vol. 10, Chapter. 6, Hadees. 1]

Narrators are trustworthy. Hadees is Authentic (Saheeh)

Imam's (as) say only what Allah (swt) says

عمر بن محمد الصيرفي عن محمد بن همام عن أحمد بن إدريس عن ابن عيسى عن علي بن النعمان، عن فضيل بن عثمان، عن محمد بن شريح قال: سمعت أبا عبد الله جعفر بن محمد عليهما السلام يقول: إن الله فرض ولايتنا، و أوجب مودتنا. والله ما نقول بأهوائنا، ولا نعمل بآرائنا، ولا نقول إلا ما قال ربنا عزوجل

Abu Hafs Umar b. Muhammad al-Sayrafi reported to me from Muhammad b. Hammam al-Askafi who reported from Ahmad b. Idrees, who reported from Ahmad b. Muhammad b. Isa al-Asha'ri, from Ali b. No-man, from Fudhail b. Uthman, from Muhammad b. Shurayh who said, I heard Abu Abdillah Jafar bin Muhammad (as) say:

"Surely, Allah has enforced our authority, and made it obligatory upon people to love us. By Allah, we do not say anything out of caprice or our desire, and we do not act according to our views. We do not say except that which our Lord, Most High, has said."

[Source: Al Amali - Sheikh Mufeed Majalis-7 Hadees-4]

http://yasoob.com/books/htm1/m013/11/no1176.html

Following the principle of validating the Hadees from the Holy Quran [See here], we find the same in the following verse of the Holy Quran:

وَمَا تَشَاءُونَ إِلَّا أَن يَشَاءَ اللَّهُ رَبُّ الْعَالَمِينَ

"And ye shall not will except as Allah wills,- the Cherisher of the Worlds." [Al Quran, 81:29]