"The lion was supposed to come there at dusk to drink."

The lion-hunt undertaken by Hadrian and Antinous was described in a contemporary poem by Pancrates of Heliopolis, supsequently quoted in the Deipnosophistai of Athenaeus (XV, 677), the text of which is available, in English translation, at http://archive.org/details/deipnosophistae01athe. A fragment of what may be Pancrates's original is included in Volume 8 of the Oxyrhynchus Papyri: http://archive.org/details/oxyrhyncuspapyr08grenuoft.

This is an extract of the Oxyrhynchus fragment;

…swifter than the steed of Adrastus, that once saved its master easily, when he was fleeing through the press of battle. On such a horse Antinous awaited the manslaying lion; in his left hand he held the bridle-rein, in his right a spear tipped with adamant. Hadrian was first to shoot forth his bronze spear; he wounded, but slew it not, for it was his intent to miss the animal, wishing to test to the full how straight the other aimed—he, lovely Antinous, son of the slayer of Argus [Hermes]. Stricken, the beast was yet more aroused; with his paws he tore the rough ground in anger; forth rose a cloud of dust, and dimmed the sunlight. He raged like a wave of the surging sea, when the West wind is awakened after the wind from Strymon [Boreas, the North Wind]. Lightly upon both he leapt, and scourged his haunches and sides with his tail, with his own dark whip…His eyes flashed dreadful fire beneath the brows; he sent forth a shower of foam from his ravening jaws to the ground, while his fangs gnashed within. From his massive head and shaggy neck the mane rose and quivered; from his other limbs it fell bushy as trees; on his back it was…like whetted spear points. In such guise he went against the glorious god Antinous, like Typhoeus of old against Zeus the Giant-Killer….