Abu Huraira reported God’s Messenger as saying, “If anyone performs a rak'a of the Morning Prayer before sunrise, he has observed the Morning Prayer; and if anyone performs a rak'a of the afternoon prayer before sunset, he has observed the afternoon prayer.” (Bukhari and Muslim.)
Hadith Referenceمشكوة المصابيح / كتاب الصلاة / 601
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 (579) و مسلم (163/ 608)»