Yahya related to me from Malik that Abu'z-Zubayr al-Makki said,"I saw the House deserted both after subh and asr, with no-one doingtawaf."Malik said, "If someone does some of his circuits andthen the subh or asr prayer is begun, he should pray with the imam andthen complete the rest of his circuits but should not pray at alluntil the sun has either risen or set "He added, "There isno harm in delaying the two rakas until after he has prayed maghrib."Malik said, "There is no harm in someone doing a single tawafafter subh or after asr, not to do more than one group of sevencircuits, and then as long as he delays the two rakas until after thesun has risen, as Umar ibn al-Khattab did, or he delays them untilafter the sun has set if it is after asr. Then when the sun has set hecan pray them if he wants, or, if he wants, he can delay them untilafter he has prayed maghrib. There is no harm in that."
USC-MSA web (English) reference: Book 20, Hadith 120
Arabic reference: Book 20, Hadith 823