The sunan prayers and their virtues - Section 2 Mishkat al-Masabih 1172
Arabic hadith text
وَعَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُصَلِّي قبل الْعَصْر رَكْعَتَيْنِ. رَوَاهُ أَبُو دَاوُد
Translation
He said that God's Messenger used to pray two rak'as before the afternoon prayer. Abu Dawud transmitted it.