‘Abdallah b. Mughaffal reported the Prophet as saying, “Pray before the sunset prayer,” adding when saying it a third time, “This applies to those who wish to do so.” That was because he did not wish the people to treat it as a sunna. (Bukhari and Muslim.)
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 1165
Hadith Gradingالألبانی:مُتَّفَقٌ عَلَيْهِ | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (1183) و مسلم (304 / 838)»