It is related that Shibli رحمة الله عليه served four hundred masters and he said, ‘I studied four thousand Traditions, then chose a single Tradition out of them, and acted in accordance with it, giving up the rest, for I meditated on it and I found my deliverance and salvation in it, the knowledge of the ancients and the moderns being all included in it I contented myself with it, and it is that the Messenger of Allah ﷺ said to one of his Companions رضي الله عنهم, “Work for your terrestrial life in proportion to your stay in it, and work for your afterlife in proportion to your eternity in it! Work for Allah in proportion to your need for Him, and work for the Fire in proportion to your ability to endure it!’”

Source: Kanz Al-Ummal, Al-Ghazali Letter to a Disciple (Ayyuha’l-Walad)