Muhammad bin Abi Ayyub (may Allah have mercy on him) said: Ibrahim (may Allah have mercy on him) said to me: Do you know the shares of inheritance (fara'id)? I said: Yes. Ibrahim (may Allah have mercy on him) said: Do you know about the shares? I said: Yes. Ibrahim (may Allah have mercy on him) said: Do you know about bequests? I said: Yes. Ibrahim (may Allah have mercy on him) said: What is your view about a man who bequeaths a third of his wealth to one person, a quarter to another and a half of his wealth to someone else? I said: That is not permissible; he is only permitted a third of his wealth. Ibrahim (may Allah have mercy on him) said: What if the heirs permit it? I said: I do not know. Ibrahim (may Allah have mercy on him) said: Shall I teach you? I said: Yes. Ibrahim (may Allah have mercy on him) said: Look for an amount that has a half, a third and a quarter. I said: That is twelve. Ibrahim (may Allah have mercy on him) said: Yes. Its half is six, its third is four and its quarter is three shares, so that makes thirteen shares. The wealth will be divided into thirteen shares: the one with the half will be given six shares, the one with the third four shares and the one with the quarter three shares. I said: Yes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12593