Hadith 1:

 حُمَيْدُ بْنُ زِيَادٍ عَنِ الْحَسَنِ بْنِ مُحَمَّدٍ عَنْ وُهَيْبِ بْنِ حَفْصٍ عَنْ أَبِي بَصِيرٍ قَالَ سَمِعْتُ أَبَا عَبْدِ اللَّهِ (عليه السلام) يَقُولُ رَحِمَ اللَّهُ عَبْداً حَبَّبَنَا إِلَى النَّاسِ وَ لَمْ يُبَغِّضْنَا إِلَيْهِمْ أَمَا وَ اللَّهِ لَوْ يَرْوُونَ مَحَاسِنَ كَلَامِنَا لَكَانُوا بِهِ أَعَزَّ وَ مَا اسْتَطَاعَ أَحَدٌ أَنْ يَتَعَلَّقَ عَلَيْهِمْ بِشَيْ‏ءٍ وَ لَكِنْ أَحَدُهُمْ يَسْمَعُ الْكَلِمَةَ فَيَحُطُّ إِلَيْهَا عَشْراً

 Narrated through a chain of reliable narrators that Abu Abd-Allah Imam Sadiq (عليه السلام) said,

"May Allah have mercy on a man who makes Us lovable to the people and does not make Us hateful to them. By Allah that if they (i.e. the Shia) were to narrate Our beautiful speech (as is without any reduction/addition/modification) they would become honored by it, and no one would be able to criticize them for anything, but one of them hears a single statement and adds in it ten (of his own words/thoughts)."

[Source: al-Kafi, Vol. 8, Pg. 229, Hadith. 293]

*Allamah Majlisi comments on the last part of the hadith saying:

قوله عليه‌السلام: « فيحط إليها » أي ينزل عليها ويضم بعضها معها عشرا من عند نفسه فيفسد كلامنا ويصير ذلك سببا لإضرار الناس لهم

As for the saying of the Imam 'he adds in it' meaning he adds ten of his own (words) to the hadith, which corrupts Our speech and becomes a reason for people to harm them.

[Source: Mirat al-Uqul, Vol. 26, Pg. 163]

Hadith 2:

أحمد بن مهران رحمه الله، عن عبد العظيم الحسني، عن علي بن أسباط، عن علي بن عقبة، عن الحكم بن أيمن، عن أبي بصير قال: سألت أبا عبد الله عليه السلام عن قول الله عز وجل: " الذين يستمعون القول فيتبعون أحسنه " إلى آخر الآية قال: هم المسلمون لآل محمد، الذين إذا سمعوا الحديث لم يزيدوا فيه ولم ينقصوا منه جاؤوا به كما سمعو

Narrated that from Abu Basir who said:

"Once I asked Abu Abd Allah Imam Sadiq (عليه السلام) about the words of Allah (عز وجل), "Those who listen to the word, then follow the best of it."(39:18)

The Imam (عليه السلام) said, "They are those who are submissive to the Family of Muhammad (عليهم السلام). It is those who when hearing a hadith do not add anything to it or remove anything from it. They present it just as they have heard."

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