It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever owes the fasts of Ramadan, let him keep them together and not make them up separately."
Abd al-Rahman bin Ibrahim is da'if (weak); he is a Madinan whom Yahya bin Ma'in, Abu Abd al-Rahman al-Nasa'i and al-Daraqutni declared weak.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8244