Zayd bin Wahb said: A man came to Sayyiduna Abdullah (bin Mas'ud) (may Allah be pleased with him) and said: O Abu Abdul-Rahman, I slept through the Fajr prayer until the sun rose. Sayyiduna Abdullah (may Allah be pleased with him) said to him: "Perform ablution in the best way you have ever performed ablution, and pray in the best way you have ever prayed." The man thought that Sayyiduna Abdullah (may Allah be pleased with him) had not grasped the gravity of what he had done. The narrator said: So he came again and said: O Abu Abdul-Rahman, I slept through the Fajr prayer until the sun rose. Sayyiduna Abdullah (may Allah be pleased with him) again said to him: "Perform ablution in the best way you have ever performed ablution, and pray in the best way you have ever prayed." He fell silent until, when the people sitting with him had thinned out, he said again: O Abu Abdul-Rahman, I slept through the Fajr prayer until the sun rose. The narrator said: Sayyiduna Abdullah (may Allah be pleased with him) took hold of his finger and squeezed it, then said: "This was said to you so that you would understand: perform ablution in the best way you have ever performed ablution, and pray in the best way you have ever prayed."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9471