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
suyuti:20533a –
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السيوطي:٢٠٥٣٣a –

"مَنِ اشْتَرى شَيئًا لَمْ يَرَهُ فَهُوَ بِالْخِيَارِ إِذَا رآهُ، إِنْ شَاءَ أَخَذَهُ وَإنْ شَاءَ تَرَكَهُ".  

[قط] الدارقطنى في السنن [ق] البيهقى في السنن وضعَّفاه عن أَبي هريرة، [حب] ابن حبّان [ق] البيهقى في السنن وضعَّفه عن مكحول مرسلًا

See similar narrations below:

Collected by Bayhaqī
bayhaqi:10428 – Abū Ḥāzim al-Ḥāfiẓ > Abū al-Faḍl Muḥammad b. ʿAbdullāh b. Muḥammad b. Khumayrawayh > Aḥmad b. Najdah > Saʿīd b. Manṣūr > Ḥammād b. Zayd > Ayyūb > al-Ḥasan

[Machine] I heard Al-Hassan say, "Whoever buys something without seeing it, then he is at a great risk if he sees it."  

البيهقي:١٠٤٢٨ – أَخْبَرَنَا أَبُو حَازِمٍ الْحَافِظُ أنا أَبُو الْفَضْلِ مُحَمَّدُ بْنُ عَبْدِ اللهِ بْنِ مُحَمَّدِ بْنِ خُمَيْرَوَيْهِ أنا أَحْمَدُ بْنُ نَجْدَةَ ثنا سَعِيدُ بْنُ مَنْصُورٍ ثنا حَمَّادُ بْنُ زَيْدٍ عَنْ أَيُّوبَ قَالَ

سَمِعْتُ الْحَسَنَ يَقُولُ مَنِ اشْتَرَى شَيْئًا لَمْ يَرَهُ فَهُوَ بِالْخِيَارِ إِذَا رَآهُ