The Messenger of Allah ﷺ said, "Shall I tell you of that by which Allah erases sins and raises ranks? Performing ablution thoroughly despite difficulties," (Ishaq said, "in difficulties,") "taking many steps to the mosques, and waiting for the next prayer after the prayer. That is the true ribat. That is the true ribat. That is the true ribat."
قال قرأت على عبد الرحمن: مالك قال أبي و حدثنا إسحاق قال حدثنا مالك عن العلاء بن عبد الرحمن عن أبيه
أن رسول الله ﷺ قال ألا أخبركم بما يمحو الله به الخطايا ويرفع به الدرجات إسباغ الوضوء على المكاره قال إسحاق في المكاره وكثرة الخطى إلى المساجد وانتظار الصلاة بعد الصلاة فذلكم الرباط فذلكم الرباط فذلكم الرباط
Its isnad is sahih. It is found in Muwatta, page 161, and it has already appeared, also from the route of Malik, at 7715, in slightly abridged form. It has also already appeared, in abridged form, from two other routes, at 7208 and 7982.