Muwatta Malik · Hadith 634

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ كَانَ يَقُولُ لاَ يَصُومُ إِلاَّ مَنْ أَجْمَعَ الصِّيَامَ قَبْلَ الْفَجْرِ ‏.‏

Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, "Only some one who makes the intention to fast before dawn (actually) fasts

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).