Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
hakim:7002 – Abū ʿAbd al-Raḥman Muḥammad b. ʿAbdullāh al-Bayrūtī > Abū Farwah from my father > Ṭalḥah b. Zayd > al-Awzāʿī > Yaḥyá b. Abū Kathīr > Anas b. Mālik

[Machine] The Prophet ﷺ said, "Whoever speaks in Persian, his wickedness increases and his integrity decreases." This narration is not authentic and its chain of transmission is weak.  

الحاكم:٧٠٠٢ – مَا حَدَّثَنَا أَبُو عَبْدِ الرَّحْمَنِ مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الْبَيْرُوتِيُّ ثَنَا أَبُو فَرْوَةَ حَدَّثَنِي أَبِي حَدَّثَنِي طَلْحَةُ بْنُ زَيْدٍ عَنِ الْأَوْزَاعِيِّ عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ

قَالَ رَسُولُ اللَّهِ ﷺ «مَنْ تَكَلَّمَ بِالْفَارِسِيَّةِ زَادَتْ فِي خُبْثِهِ وَنَقَصَتْ مِنْ مُرُوءَتِهِ» ليس بصحيح وإسناده واه بمرة  

See similar narrations below:

Collected by Suyūṭī
suyuti:21157a –
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السيوطي:٢١١٥٧a –

"مَنْ تَكَلَّمَ بِالْفَارسِيَّةِ زَادَتْ في خَبِّه وَنقَصَتْ مِن مُرُوءَتِهِ".  

[عد] ابن عدى في الكامل [ك] الحاكم في المستدرك وتعقب عن أَنس، أورده ابن الجوزي في الموضوعات