(30) باب مَنْ أَدْرَكَ رَكْعَةً مِنَ الصَّلاَةِ فَقَدْ أَدْرَكَ تِلْكَ الصَّلاَةَ
Abu Huraira reported the Messenger of Allah (ﷺ) as saying:
He who finds a rak'ah of the prayer, he in fact finds the prayer.
Reference: Sahih Muslim 607 a
In-book reference: Book 5, Hadith 205
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1260