Al-Sha'bi (may Allah have mercy on him) said: Ibn Abbas (may Allah be pleased with them both) wrote from Basrah to Sayyiduna Ali (may Allah be pleased with him) about (a case of) six brothers and a grandfather, and Ali (may Allah be pleased with him) replied: Give him a seventh of the wealth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12439