Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The mother of Sa'd (may Allah be pleased with him) began to say: "Alas for Sa'd, how sensible and diligent he was!" the Prophet (peace and blessings be upon him) said to her: "Do not say more than this. By Allah! As far as I know, he was sensible in his affairs and strong in the affair of Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5309