As-salaamu `alaykum...
Ankle to ankle/heel to heel was the action of the companions, not necessarily reported from the Prophet sal-Allaahu `alayhi wasallam. There are a few hadeeth in Bukhaaree about the topic...
An-Nu`maan Ibn Basheer, may Allaah be pleased with him said,
"I saw that every one of us used to put his heel with the heel of his companion." [Saheeh Al-Bukhaaree, Book of the Charactertics of the Prayer]
There is also a similar saying from Anas, and similar was reported on Bilaal (though not sure if in Saheeh Al-Bukhaaree), may Allaah be pleased with them both. But I must stress akhee, to look into how the salaf, the early scholars, understood these ahaadeeth. The reason I'm saying this, is because nowadays, people do strange things in order to act upon these ahaadeeth, like standing so wide apart that they look like they're going to do the splits...