The speed and movements that nullify one’s Prayer are those that make the Prayer as if it was not Prayer. As for your saying that the imam performed the Prayer hurriedly, you do not say when you mean by hurriedly. It may be that you are used to offering the Prayer deliberately, which is worthy of praise in itself, yet the imam intended to lighten it so that it would not become a burden on the Muslims who follow him. If the imam does so, this is not regarded as speed that nullifies the Prayer, nor does this affect the concentration (khushu`) of the imam in Prayer.
Khushu` in Prayer is required. Some scholars believe that it is one of the pillars of Prayer, and so, if it is missing, the Prayer will be invalid. But this point, that is, whether it is a pillar of the Prayer, is controversial among scholars.
Anyway, mind that it does not follow from one’s performing the Prayer hurriedly that one has not been humble while praying. One may say only one of the many statements of glorification during Prayer sincerely, and Allah Almighty accepts one’s Prayer just for being sincere at saying that statement.
It is noteworthy that performing Prayer is an easy task to do. One can maintain khushu` during Prayer without having to prolong it. Allah Almighty has required the believers to maintain khushu` in Prayer. He Almighty has not asked them to prolong it. Almighty Allah says in that regard: “Successful indeed are the believers, who are humble in their Prayers.” (Al-Muminun: 1-2)
Moreover, some of the Companions of the Prophet (peace and blessings be upon him) would lighten Prayer so that they might not have doubts about having performed it correctly. For example, it was narrated that `Ammar ibn Yasir (may Allah be pleased with him) offered two rakahs of Prayer lightly. Seeing him doing so, `Abdur-Rahman ibn Al-Harith (may Allah be pleased with him) said to him, “You have lightened them, Abu Al-Yaqzhan!” `Ammar (may Allah be pleased with him) said, “I did so deliberately lest I have any doubts (about its correctness). I heard Allah’s Messenger (peace and blessings be upon him) saying: ‘One may perform one Prayer and it is only its tenth or ninth or eighth or seventh or sixth, etc, that is Accepted.’”
Khushu` in Prayer can be achieved by directing all one’s attention to being sincere heart and soul to Allah Almighty, and not making a lot of extraneous movements during the Prayer. Making few movements is not a sign of being insincere.
It was reported by Al-Baihaqi that `Umar ibn Hurayth said, “Allah’s Messenger (peace and blessings be upon him) might touch his beard while performing Prayer.”
Furthermore, it is recommended in Shari`ah that one who is to lead a congregation in Prayer lighten it in a way that wouldn’t render it invalid or lead to its being void of khushu`. It is reported on the authority of Abu Hurayrah (may Allah be pleased with him) that Allah’s Messenger (peace and blessings be upon him) said, “If one amongst you leads a group of people in Prayer, one should shorten it because among them there are the sick the weak and the needy (having some jobs to do). And when one prays alone, one can prolong the Prayer however one wants.”
It was also reported by Ibn Mas`ud (may Allah be pleased with him): “A man came and said, ‘O Allah’s Messenger! I keep away from the morning Prayer because so-and-so (imam) prolongs it too much.’ Allah’s Messenger (peace and blessings be upon him) became furious and I had never seen him more furious than he was on that day. The Prophet (peace and blessings be upon him) then said: ‘O people! Some of you make others dislike the Prayer, so whoever becomes an imam he should lighten the Prayer, as behind him are the weak, the old and the needy.’”
Prolonging or shortening the time of doing something is relative to people. Some may regard the time of doing something long while others consider it short. Hence, some scholars said that if an imam knows that his followers like him to prolong the Prayer, he could do that. For example, if a group of people have gathered to offer the Night Vigil Prayer, their imam can prolong the Prayer then. Although this may exhaust them, they have gathered voluntarily for the very purpose of doing it, and this implies that they want to prolong it.
According to some scholars, a Muslim is not to utter more than three statements of glorification during bowing and prostrating in Prayer. However, it was reported that the Prophet (peace be upon him) would glorify Allah more than that during bowing and prostrating. The scholars said that the Prophet’s Companions (may Allah be pleased with them all) would like that the Prayer behind the Prophet (peace be upon him) be long.
Anas ibn Malik (may Allah be pleased with him) reported, “I never prayed behind any imam a Prayer lighter and more perfect than that behind the Prophet, and he used to cut short the Prayer whenever he heard the cries of a child lest he should put the child’s mother to trial.”
Abu Qilaba `Abdullah ibn Zaid Al-Jurami Al-Basri is reported to have said, “Once, Malik ibn Huwairith came to this mosque and said: ‘I sometimes lead you in Prayer at times other than that of the compulsory Prayers in order to show you how the Prophet (peace and blessings be upon him) used to pray.’ Upon that, one asked Abu Qilaba, ‘How did he (Malik ibn Huwairith) use to pray?’ Abu Qilaba replied, ‘(He would pray) like this sheikh of ours (Abu Yazid).’ (Abu Yazid used to sit (for a while) on raising his head from the second prostration before getting up).”
All in all, imams are required to perform the Prayer perfectly, yet lighten it at the same time (so that it does not become a burden on the persons who pray behind them). However, the imams can prolong the Prayer if the people who pray behind them so like. The point is that the imams should not pray in such a hurried way that may make the people who pray behind them feel they are not in Prayer. He who prays by himself can prolong the Prayer however he likes. Bear in mind that the congregational Prayer differs from the individual one in that respect.